全文获取类型
收费全文 | 1148篇 |
免费 | 70篇 |
专业分类
1218篇 |
出版年
2023年 | 6篇 |
2022年 | 14篇 |
2021年 | 30篇 |
2020年 | 25篇 |
2019年 | 19篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 48篇 |
2014年 | 41篇 |
2013年 | 62篇 |
2012年 | 73篇 |
2011年 | 105篇 |
2010年 | 60篇 |
2009年 | 44篇 |
2008年 | 56篇 |
2007年 | 68篇 |
2006年 | 74篇 |
2005年 | 68篇 |
2004年 | 50篇 |
2003年 | 39篇 |
2002年 | 42篇 |
2001年 | 21篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1968年 | 4篇 |
排序方式: 共有1218条查询结果,搜索用时 8 毫秒
991.
Toni Schmid 《Ethnos》2013,78(1-2):74-94
Irrigation's Impact on Society. Theodore E. Downing &; McGuire Gibson (eds.), Anthropological Papers of The University of Arizona Number 25. Tucson, 1974, 181 pp. Women: An Anthropological View. Evelyn S. Kessler. Holt, Rinehart and Winston, New York etc. 1976, 267 pp. A History of Ethnology. Fred W. Voget. Holt, Rinehart and Winston, New York etc. 1975. ix + 879 pp. US $ 17.95. Music in the Culture of Northern Afghanistan. Mark Slobin. Viking Fund Publications in Anthropology 54. Tucson: The University of Arizona press 1976. xiv + 297 pp., 8 maps, 56 illustrations, bibliography and index. Java‐Masken. Der Tanz auf einem Bein. Heinz Lucas. Erich Röth Verlag. Kassel. 1973, pp. 347, ill. 相似文献
992.
Anna Toledo Toni Karppinen Maija E. Miettinen Juhani Leppäluoto Olli Vuolteenaho Lasse Ylianttila 《Chronobiology international》2013,30(11):1570-1580
ABSTRACTThe evening chronotype is associated with psychological symptoms such as depressed mood, while skin exposure to ultraviolet radiation (UVR) may affect mood and behavior through neural and humoral routes. This pilot study aimed to investigate the impact of whole-body narrow-band (NB) UV-B exposure on current mood state and circulating 25-hydroxyvitamin D3 (25(OH)D3), interleukin-6 (IL-6), cortisol and β-endorphin (β-END) levels in healthy participants. Here, eleven healthy women received full-body NB UV-B exposures on four afternoons, and the chronotype was assessed with a shortened version of Horne and Östberg’s Morningness-Eveningness Questionnaire (MEQ). Perceived mood was evaluated using the Visual Analogue Scale (VAS), and serum 25(OH)D3, IL-6, cortisol and β-END concentrations were monitored daily. Decreasing VAS values showed mood to improve significantly over the five days after the four suberythematous NB UV-B exposures (p = .038), and the more the circadian preference was inclined toward eveningness, the greater the improvement in the mood dimension of wellbeing (p = .021). Baseline mood state was correlated with baseline 25(OH)D3 (r = ?0.54, 95% CI: ?0.86 to ?0.09) and with baseline cortisol (r = ?0.57, 95% CI: ?0.87 to ?0.04). During the NB UV-B exposures, 25(OH)D3 increased significantly, as expected, and IL-6 declined significantly by ?0.35 (95% CI: ?0.69 to ?0.07) pg/mL from the initial values of 1.12 ± 0.66 pg/mL (p = .025). In conclusion, in our pilot study, NB UV-B exposure improved mood, especially among those with evening preference for their daily activities, as well as circulating 25(OH)D3 levels, whereas circulating IL-6 levels decreased.Abbreviations: UVR: Ultraviolet radiation; NB UV-B: narrow-band UV-B; VAS: Visual Analogue Scales; β-END: β-endorphin; IL-6: Interleukin-6 相似文献
993.
Host specificity testing to predict host range is one of the key steps to predicting the risk a biological control agent will present to non-target organisms in the new environment. When host specificity testing data contain discrepancies, or unacceptable levels of uncertainty, it can be difficult for decision-makers to adequately address this uncertainty. To better understand the uncertainty in host specificity testing, we used a range of statistical tools to examine a data set associated with the leaf weevil Cleopus japonicus (Curculionidae), a biological control agent for the weed Buddleja davidii (Buddlejaceae) in New Zealand. Significant uncertainty arose during the early stages of host specificity testing when one C. japonicus larva reared to pupation on a culturally important native plant. Further trials were conducted to evaluate the suitability of C. japonicus as a biological control agent, and despite the uncertainty, C. japonicus was released in New Zealand in 2006, and has since established populations at each release site. However, the possibility of larvae completing their life cycle on the native plant initiated this evaluation of the statistics associated with testing biological control agents. We present results from analyses of the C. japonicus survival data using confidence intervals, equivalence testing, power analyses and survival curves to highlight the appropriateness of each of these tools for interpreting host specificity tests in biological control. 相似文献
994.
Toni Nikolić Oleg Antonić Antun L. Alegro Iva Dobrović Sandro Bogdanović Zlatko Liber 《Plant biosystems》2013,147(3):435-445
Abstract The European Mediterranean region is one of the world's major centres of biodiversity. Research on plant species diversity in this region has neglected the area along the eastern part of the Adriatic basin in comparison to the other Mediterranean areas. The main aim of this study was to focus on this neglected area, by supplying data which is at present lacking in order to discuss the species-area relationship (SAR), floristic richness and endemism of the Adriatic islands and coast. Floristic data for 106 Croatian islands collected by different authors were integrated, systematised and presented in a form usable by other researchers worldwide. The Power (Arrhenius) function was used for modelling (by non-linear regression) the SAR. Residuals around the regression curve (as indicators of floristic diversity without the influence of island area) were calculated for each island. The proportion of endemics in the total island flora varies from 0% up to 28.6%, and 17.5% for narrow endemics. Floristic richness of the broader region was estimated (on the basis of SAR extrapolation) on 1807 species for all Croatian islands, and on 2797 species for the entire Mediterranean area in Croatia. 相似文献
995.
Experimental evidence of negative interference in Daphnia magna 总被引:5,自引:0,他引:5
Individuals of Daphnia magna Straus living together in groups were found to influence each other in a density-dependent manner. The effect appeared as an inhibition in offspring production and was demonstrated to be induced in part or completely by metabolic products released by Daphnia itself (negative interference). Negative interference was measurable even when there were only two individuals in 50 ml medium (40 animals · 1–1) and increased up to a density of six animals per 50 ml (120 animals · 1–1). Also, animals living singly in Daphnia-conditioned water showed a decrease in reproduction. For the measurements a cascade of vessels was developed in which flow-through conditions ensured a constant concentration of algae throughout the system. 相似文献
996.
We have examined production of mediumchain fatty acids by Brassica napus L. plants transformed with a California bay (Umbellularia californica) medium-chain acyl-acyl carrier protein (ACP) thioesterase (UcFatB1) cDNA under the control of the constitutive cauliflower mosaic virus 35S promoter. These plants were found to accumulate medium-chain fatty acids in seeds but not in leaves or roots. Assay of thioesterase activity in extracts of leaves indicated that lauroyl-ACP thioesterase activity is comparable to oleoyl-ACP thioesterase (EC 3.1.2.14) activity in transformant leaves. Furthermore, leaf lauroyl-ACP thioesterase activity was in excess of that which produced a significant increase in the amount of laurate (12:0) in seed. Studies in which isolated chloroplasts were 14C-labelled were used to evaluate whether medium-chain fatty acids were produced in transformed leaves. Up to 34% of the fatty acids synthesized in vitro by isolated chloroplasts were 12:0. These results demonstrate that the normally seed-localized lauroyl-ACP thioesterase can be expressed in active form in leaves, imported into chloroplasts and can access acyl-ACP intermediates of leaf de-novo fatty acid synthesis. The most likely explanation for the lack of accumulation of 12:0 in transformed leaves is its rapid degradation by -oxidation. In support of this hypothesis, isocitrate lyase (EC 4.1.3.1) activity was found to be significantly increased in plants transformed with 35S-UcFatB1.Abbreviations ACP
acyl carrier protein
- CaMV
cauliflower mosaic virus
- control
Brassica napus cultivar 212/86
- event 8
pCGN3831-212/86-8
- event 11
pCGN3831-212/86-11
- FAS
fatty acid synthase
- IL
isocitrate lyase
- KAS
-keto-acyl ACP synthase
- MS
malate synthase
- OTE
oleoyl-ACP thioesterase
- TAG
triacylglycerol
-
UcFatB1
California bay medium-chain acyl-ACP thioesterase
We are indebted to Calgene's Brossica-transformation, growth-chamber, greenhouse, and lipid-analysis personnel. Maelor Davies conducted the initial tranformant analysis. We thank Laura Olsen for IL and MS Western blot analysis and advice on IL and MS activity assays. This work was supported in part by a grant from the U.S. Department of Energy (No. DE-FG02-87ER12729). Acknowledgement is made to the Michigan Agricultural Experiment Station for its support of this research. 相似文献
997.
Jungas T Verbeke P Darville T Ojcius DM 《Microbes and infection / Institut Pasteur》2004,6(13):1145-1155
Infection by a number of Chlamydia species leads to resistance of the host cell to apoptosis, followed by induction of host-cell death. In a population of infected cells that displays protection against staurosporine-induced apoptosis among the adherent cells, we find that cells that had been recovered from the supernatant share characteristics of both apoptosis and necrosis, as assayed by the propidium iodide (PI)-annexin V double-labeling technique. Cell death was observed in both an epithelial cell line and primary fibroblasts, although the primary cells had a higher propensity to die through apoptosis than the immortalized cell line. Staurosporine-mediated activation of the pro-apoptotic BCL-2 family member, BAX, was inhibited in the epithelial cell line infected for 32 h with the lymphogranuloma venereum (LGV/L2) but not the murine pneumonitis (MoPn) strain of C. trachomatis, but inhibition of staurosporine-mediated BAX activation disappeared after 48 h of infection with the LGV/L2 strain. Conversely, infection with MoPn (C. muridarum) but not LGV/L2 led to BAX activation after 72 h, as previously reported for shorter (48 h) infection with the guinea pig inclusion conjunctivitis (GPIC) serovar of C. psittaci (C. caviae). These results suggest that the ability to inhibit staurosporine-mediated BAX activation or to activate BAX due to the infection itself may vary as a function of the chlamydial strain. Interestingly, both the epithelial cells and the fibroblasts also released high mobility group box 1 protein (HMGB1) during infection, although much less HMGB1 was released from fibroblasts, consistent with the higher level of apoptosis observed in the primary cells. HMGB1 is released preferentially by necrotic or permeabilized viable cells, but not apoptotic cells. In the extracellular space, HMGB1 promotes inflammation through interaction with specific cell-surface receptors. Higher levels of HMGB1 were also measured in the genital-tract secretions of mice infected vaginally with C. trachomatis, compared to uninfected controls. These results suggest that cells infected with Chlamydia release intracellular factors that may contribute to the inflammatory response observed in vivo. 相似文献
998.
999.
Margaret F. Roberts David McCarthy Toni M. Kutchan Carmine J. Coscia 《Archives of biochemistry and biophysics》1983,222(2):599-609
In continuing studies on the metabolic activity of Papaver somniferum, latex has been examined for its enzyme and alkaloidal metabolite content. After an initial centrifugation of latex at 1000g, the pellet which contained a heterogeneous population of dense organelles was further resolved on sucrose gradients. Of the enzymes monitored, acid phosphatase and l-3,4-dihydroxyphenylalanine decarboxylase were found to be in the latex 1000g supernatant, whereas catecholase (polyphenolase) was localized in two distinct organelles within the 1000g sediment. The lighter organelles, sedimenting at 30% sucrose, contained a soluble enzyme which was readily released on organelle plasmolysis, whereas the catecholase found within the heavier organelles, sedimenting at 55–60% sucrose, was membrane bound and showed significant activity only in the presence of Triton X-100. These latter organelles also contained the alkaloids, including morphine and thebaine, and were observed to readily accumulate [14CH3]morphine. The alkaloid precursor, dopamine, was localized in the same dense vesicle fraction as the alkaloids. The rate of uptake of [7-14C]dopamine into these fractions at room temperature, however, was markedly lower than that of morphine. Electron microscopic examination of the organelles of various densities revealed that they possessed different morphology. The results are consistent with the concept that both the 1000g and supernatant fractions of the latex are required for alkaloid biosynthesis and that a sub-population of dense organelles found in the 1000g sediment have at least a function as a storage compartment for both alkaloids and their catecholamine precursor. 相似文献
1000.
Lee TM Farrow MF Arnold FH Mayo SL 《Protein science : a publication of the Protein Society》2011,20(11):1935-1940
Interest in generating lignocellulosic biofuels through enzymatic hydrolysis continues to rise as nonrenewable fossil fuels are depleted. The high cost of producing cellulases, hydrolytic enzymes that cleave cellulose into fermentable sugars, currently hinders economically viable biofuel production. Here, we report the crystal structure of a prevalent endoglucanase in the biofuels industry, Cel5A from the filamentous fungus Hypocrea jecorina. The structure reveals a general fold resembling that of the closest homolog with a high-resolution structure, Cel5A from Thermoascus aurantiacus. Consistent with previously described endoglucanase structures, the H. jecorina Cel5A active site contains a primarily hydrophobic substrate binding groove and a series of hydrogen bond networks surrounding two catalytic glutamates. The reported structure, however, demonstrates stark differences between side-chain identity, loop regions, and the number of disulfides. Such structural information may aid efforts to improve the stability of this protein for industrial use while maintaining enzymatic activity through revealing nonessential and immutable regions. 相似文献