全文获取类型
收费全文 | 336554篇 |
免费 | 34425篇 |
国内免费 | 182篇 |
专业分类
371161篇 |
出版年
2018年 | 2858篇 |
2017年 | 2703篇 |
2016年 | 3934篇 |
2015年 | 5349篇 |
2014年 | 6242篇 |
2013年 | 8768篇 |
2012年 | 10005篇 |
2011年 | 9973篇 |
2010年 | 6800篇 |
2009年 | 6144篇 |
2008年 | 8858篇 |
2007年 | 9311篇 |
2006年 | 8601篇 |
2005年 | 8299篇 |
2004年 | 8014篇 |
2003年 | 7778篇 |
2002年 | 7780篇 |
2001年 | 18147篇 |
2000年 | 18371篇 |
1999年 | 14103篇 |
1998年 | 4233篇 |
1997年 | 4499篇 |
1996年 | 4304篇 |
1995年 | 4012篇 |
1994年 | 3945篇 |
1993年 | 3781篇 |
1992年 | 11489篇 |
1991年 | 11125篇 |
1990年 | 10680篇 |
1989年 | 10243篇 |
1988年 | 9483篇 |
1987年 | 8845篇 |
1986年 | 8079篇 |
1985年 | 7967篇 |
1984年 | 6394篇 |
1983年 | 5567篇 |
1982年 | 4107篇 |
1981年 | 3592篇 |
1980年 | 3355篇 |
1979年 | 6115篇 |
1978年 | 4575篇 |
1977年 | 4125篇 |
1976年 | 3765篇 |
1975年 | 4333篇 |
1974年 | 4498篇 |
1973年 | 4394篇 |
1972年 | 4092篇 |
1971年 | 3508篇 |
1970年 | 3174篇 |
1969年 | 2975篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
P.A. Wadegaonkar K.A. Bhagwat M.K. Rai 《Plant Cell, Tissue and Organ Culture》2006,84(2):100202-100204
Direct rooting from leaf explants of Withania somnifera was achieved on half strength Murashige and Skoog’s medium supplemented with 15 g l−1 sucrose, and different concentrations of growth regulators. Basal medium supplemented with 2.85 μM indoleacetic acid and
9.85 μM indolebutyric acid achieved maximum number of roots with 100% response. The roots were cultured on MS liquid medium
for the establishment of root-organ culture with the same plant growth regulators and incubated on an orbital shaker at 80 rpm
at 25 ± 2 °C. A root biomass of 6.15 ± 0.17 g was obtained after 5 weeks. When 1 g roots were inoculated to 2.5 l bubble column
reactor, 47 g roots were obtained after 6 weeks. The concentration of alkaloids was increased as compared to field grown roots.
The maximum concentration of withanolides (10 mg g−1 dry weight) was obtained in the bioreactor. 相似文献
182.
In order to investigate the pharmacological basis of ‘Yang-invigorating’ action, the effect of oral treatment with the methanolic extract of ‘Yang-invigorating’ herbs on ATP-generation capacity was examined, using heart homogenates prepared from herb-pretreated mice. Tonifying (i.e., health-promoting) herbs of other functional categories were also included for comparison. The results indicated that ‘Yang-invigorating’ Chinese tonifying herbs could invariably enhance myocardial ATP-generation capacity, with the extent of stimulation varying among the herbs. In contrast, ‘Yin-nourishing’ herbs either did not stimulate or even decreased myocardial ATP-generation capacity. While ‘Qi-invigorating’ herbs produced variable effects on myocardial ATP-generation capacity, most of the ‘blood-enriching’ herbs did not cause any significant changes. The results obtained from studies using myocardial mitochondrial fractions isolated from herb-pretreated mice suggest that ‘Yang-invigorating’ herbs might speed up ATP generation by increasing mitochondrial electron transport. The ensemble of results has provided evidence for the first time to support the pharmacological basis of ‘Yang invigoration’ in Chinese medicine. 相似文献
183.
Hypoglycemic activity of polysaccharide, with antioxidation, isolated from cultured Cordyceps mycelia 总被引:8,自引:0,他引:8
S.P. Li G.H. Zhang Q. Zeng Z.G. Huang Y.T. Wang T.T.X. Dong K.W.K. Tsim 《Phytomedicine》2006,13(6):428-433
Cordyceps sinensis, a well-known traditional Chinese medicine, possesses anti-tumor, immunostimulant and antioxidant activities; however, the identities of active components have not been determined. In our previous study using antioxidant activity-guided fractionation [Li et al., 2003. A polysaccharide isolated from Cordyceps sinensis, a traditional Chinese medicine, protects PC12 cells against hydrogen peroxide-induced injury. Life Sci. 73, 2503-2513], a polysaccharide of molecular weight approximately 210kDa was isolated from cultured Cordyceps mycelia by ion-exchange and sizing chromatography. The isolated polysaccharide, named CSP-1, which has strong anti-oxidation activity, contains glucose, mannose and galactose in the ratio of 1:0.6:0.75. In the present study, we demonstrated the hypoglycemic effect of CSP-1 on normal and alloxan-diabetic mice and streptozotocin (STZ)-diabetic rats. The basal glucose level did not differ significantly among the normal mice. CSP-1 (at 200 and 400mg/kg body wt./day for 7 days, p.o.), however, significantly reduced the blood glucose level by 12.0+/-3.2% and 22.5+/-4.7% in normal mice, respectively (p<0.05). When administered at a dose of higher than 200mg/kg body wt. daily for 7 days, CSP-1 produced a significant drop in blood glucose level in both STZ-induced diabetic rats and alloxan-induced diabetic mice. The serum insulin levels in diabetic animals were also increased by administration of CSP-1 (p<0.05). CSP-1 with hypoglycemic properties increased circulating insulin level in diabetic animals, which suggests that CSP-1 may stimulate pancreatic release of insulin and/or reduce insulin metabolism. 相似文献
184.
Hamed K. Abbas Robert M. Zablotowicz H. Arnold Bruns Craig A. Abel 《Biocontrol Science and Technology》2006,16(5):437-449
The ability of two non-aflatoxigenic Aspergillus flavus Link isolates (CT3 and K49) to reduce aflatoxin contamination of corn was assessed in a 4-year field study (2001–2004). Soil was treated with six wheat inoculant treatments: aflatoxigenic isolate F3W4; two non-aflatoxigenic isolates (CT3 and K49); two mixtures of CT3 or K49 with F3W4; and an autoclaved wheat control, applied at 20 kg ha?1. In 2001, inoculation with the aflatoxigenic isolate increased corn grain aflatoxin levels by 188% compared to the non-inoculated control, while CT3 and K49 inoculation reduced aflatoxin levels in corn grain by 86 and 60%, respectively. In 2002, the non-toxigenic CT3 and K49 reduced aflatoxin levels by 61 and 76% compared to non-inoculated controls, respectively. In 2001, mixtures of aflatoxigenic and non-aflatoxigenic isolates had little effect on aflatoxin levels, but in 2002, inoculation with mixtures of K49 and CT3 reduced aflatoxin levels 68 and 37% compared to non-inoculated controls, respectively. In 2003 and 2004, a low level of natural aflatoxin contamination was observed (8 ng g?1). However, inoculation with mixtures of K49?+?F3W4 and CT3?+?F3W4, reduced levels of aflatoxin 65–94% compared to the aflatoxigenic strain alone. Compared to the non-sclerotia producing CT3, strain K49 produces large sclerotia, has more rapid in vitro radial growth, and a greater ability to colonize corn when artificially inoculated, perhaps indicating greater ecological competence. Results indicate that non-aflatoxigenic, indigenous A. flavus isolates, such as strain K49, have potential use for biocontrol of aflatoxin contamination in southern US corn. 相似文献
185.
J. H. Kim B. C. Campbell R. Molyneux N. Mahoney K. L. Chan J. Yu J. Wilkinson J. Cary D. Bhatnagar T. E. Cleveland 《Mycotoxin Research》2006,22(1):3-8
It was initially shown that gallic acid, from hydrolysable tannins in the pelliele of walnut kernels, dramatically inhibits
biosynthesis of aflatoxin byAspergillus flavus. The mechanism of this inhibition was found to take place upstream from the gene cluster, including the regulatory gene,aflR, involved in aflatoxin biosynthesis. Additional research using other antioxidant phenolics showed similar antiaflatoxigenic
activity to gallic acid. Treatment ofA. flavus withtert-butyl hydroperoxide resulted in an almost doubling of aflatoxin biosynthesis compared to untreated samples. Thus, antioxidative
response systems are potentially useful molecular targets for control ofA. flavus. A high throughput screening system was developed using yeast,Saccharomyces cerevisiae, as a model fungus. This screening provided an avenue to quickly identify fungal genes that were vulnerable to treatment
by phenolic compounds. The assay also provided a means to quickly assess effects of combinations of phenolics and certain
fungicides affecting mitochondrial respiration. For example, theS. cerevisiae sod2† mutant was highly sensitive to treatment by certain phenolics and strobilurins/antimycin A, fungicides which inhibit complex
III of the mitochondrial respiratory chain. Verification of stress to this system in the target fungus,A. flavus, was shown through complementation analysis, wherein the mitochondrial superoxide dismutase (Mn-SOD) gene (sodA) ofA. flavus in the ortholog mutant,sod2†, ofS. cerevisiae, relieved phenolic-induced stress. Mitochondrial antioxidative stress systems play an important role in fungal response to
antifungals. Combined treatment of fungi with phenolics and inhibitors of mitochondrial respiration can effectively suppress
growth ofA. flavus in a synergistic fashion. 相似文献
186.
Variation in Plant Substrates and its Consequences for Insect Vibrational Communication 总被引:2,自引:0,他引:2
R. B. Cocroft H. J. Shugart K. T. Konrad & K. Tibbs 《Ethology : formerly Zeitschrift fur Tierpsychologie》2006,112(8):779-789
Many insects and other arthropods communicate using plant‐borne vibrational signals. Vibration transmission along plant stems imposes a frequency filter on signals, and may cause signal degradation from reflected waves. Furthermore, different plant species and plant parts can differ in their transmission properties. This variability in the communication channel may constrain the reliability of signals, with important consequences for the evolution of vibrational communication systems, as well as for researchers studying signal variation at an individual, population, or species level. In this study we estimate the magnitude of substrate‐related variation in the mate advertisement signals of a treehopper (Hemiptera: Membracidae: Umbonia crassicornis). We used laser vibrometry to record the signals produced by 25 adult males on two different plant species, one host and one non‐host. We recorded male signals on two plants per species; within each plant, signals were recorded simultaneously at two distances. We measured three spectral characteristics (dominant frequency, relative amplitude of the signals’ high and low frequency components, frequency at the end of the signal) and two temporal characteristics (signal duration and click repetition rate). Spectral characteristics were influenced by the distance at which the signal was recorded, and this influence varied among plant species and individuals. Temporal characteristics were less influenced, although signal length was influenced by distance, an effect that varied among individual plants. Overall, the magnitude of the effects was small. Furthermore, there was significant within‐individual repeatability of almost all signal traits across different plant substrates. Signal characteristics were thus reliably associated with individuals, even when they signaled on different plants. 相似文献
187.
188.
The Everglades Nutrient Removal Project 总被引:1,自引:0,他引:1
189.
The occurrence of functional chloroplasts in internal stem tissues and their distribution profiles in 20 woody species have been investigated. Chloroplasts were identified from the red chlorophyll auto-fluorescence using epi-fluorescence microscopy. Chloroplasts were detected in the cortex of all species examined, in the xylem rays of 19 and in the perimedullar and the pith cells of 16 out of the 20 investigated species. Chloroplast containing cell clusters in the pith were identified in some species. In addition, we report on the semi-quantitative distribution of chlorophylls in various internal stem tissues. Chlorophyll level was estimated by reflectance measurements at specific wave bands. Although decreasing chlorophyll gradients from cortex to pith were observed in half of the species, chlorophyll distribution in the remaining species was irregular with occasionally high levels in the pith. According to our data, chlorophyll occurrence in stem internal tissues is quite widespread, even in the light remote, deeply shaded central compartments like pith, provided that corresponding cells are viable. The species-specific tissue distribution of chlorophyll levels may be used to select suitable plants to investigate further this neglected area of photosynthesis research. 相似文献
190.
K. I. Gubaev T. R. Nasibullin A. N. Zakirova O. E. Mustafina 《Russian Journal of Genetics》2006,42(12):1447-1451
Polymerase chain reaction was used to study the association of polymorphic markers I/D of the angiotensin-converting enzyme gene (ACE) and A1166C of the angiotensin II type 1 receptor gene (AT2R1) with chronic heart failure (CHF) in Russian and Tatar patients that had had myocardial infarction. In Russian patients aged 50 years or younger that had had macrofocal myocardial infarction, the CC genotype of the A1166C polymorphic marker of gene AT2R1 was associated with an increased risk of CHF (OR = 11.36). Genotype DD and allele D of the I/D polymorphic marker of gene ACE were associated with a more severe CHF (functional class III–IV) in Russian patients (OR = 3.50 and 2.06). In Tatar patients, polymorphic markers I/D of gene ACE and A1166C of gene AT2R1 were not associated with CHF. 相似文献