全文获取类型
收费全文 | 13090篇 |
免费 | 1122篇 |
国内免费 | 7篇 |
出版年
2022年 | 84篇 |
2021年 | 167篇 |
2020年 | 88篇 |
2019年 | 146篇 |
2018年 | 131篇 |
2017年 | 117篇 |
2016年 | 262篇 |
2015年 | 451篇 |
2014年 | 499篇 |
2013年 | 693篇 |
2012年 | 820篇 |
2011年 | 839篇 |
2010年 | 532篇 |
2009年 | 509篇 |
2008年 | 725篇 |
2007年 | 733篇 |
2006年 | 640篇 |
2005年 | 703篇 |
2004年 | 678篇 |
2003年 | 615篇 |
2002年 | 608篇 |
2001年 | 115篇 |
2000年 | 96篇 |
1999年 | 121篇 |
1998年 | 171篇 |
1997年 | 112篇 |
1996年 | 104篇 |
1995年 | 91篇 |
1994年 | 92篇 |
1993年 | 88篇 |
1992年 | 96篇 |
1991年 | 86篇 |
1990年 | 82篇 |
1989年 | 70篇 |
1988年 | 75篇 |
1987年 | 84篇 |
1986年 | 86篇 |
1985年 | 81篇 |
1984年 | 123篇 |
1983年 | 99篇 |
1982年 | 123篇 |
1981年 | 130篇 |
1980年 | 144篇 |
1979年 | 111篇 |
1978年 | 103篇 |
1977年 | 108篇 |
1976年 | 85篇 |
1975年 | 84篇 |
1974年 | 93篇 |
1973年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Competition of cyclooctenes and cyclooctadienes for ethylene binding and activity in plants 总被引:1,自引:0,他引:1
trans-Cyclooctene, cis,trans-1,5-cyclooctadiene, and cis,trans-1,3-cyclooctadiene have been compared with the cis and cis,cis isomers and with 2,5-norbornadiene for competition with ethylene for binding in mung bean sprouts and tobacco and for action (induction of chlorophyll degradation) in banana. The compounds containing a trans double bond were much more effective in competition for binding and action than the cis and cis,cis compounds. trans-Cyclooctene and cis,trans-1,3-cyclooctadiene were in the general range of 50–90 times more effective than 2,5-norbornadiene.R.J. Reynolds Research Apprentice 相似文献
142.
Dr. Edward B. Blanchard Peter J. Cornish David A. Wittrock Steve Fahrion 《Applied psychophysiology and biofeedback》1990,15(2):145-159
Reports of subjective experiences of 73 hypertensive patients who were treated with thermal biofeedback for hand warming were obtained over 16 treatment sessions. Most of the differential responding in subjective report occurred in the first 5 sessions. Differences in reports of throbbing were associated with medication status during treatment (presence of sympatholytic antihypertensive agent). From 4 to 9% of patients report negative subjective experiences at any one session. When short-term clinical successes (either elimination of medication or reduction of BP) were compared with short-term failures, it was found that successes reported more warmth, more likelihood of falling asleep, and more dreamlike experiences. The latter were more likely to occur suddenly for the successes. Correlational analyses revealed consistent positive associations between reports of warmth and relaxation with highest temperature achieved in the session and consistent negative associations between experiencing physical sensations and degree of temperature change within the session.This research was supported in part by grants from NHLBI, HL-27622 and HL-31189. 相似文献
143.
T. C. Hsu Edward J. Shillitoe Lorraine M. Cherry Qi Lin Stimson P. Schantz Cynthia Furlong 《In vitro cellular & developmental biology. Plant》1990,26(1):80-84
Summary Forty lymphoblastoid (lymphoid) lines were established from 42 volunteer blood donors, including healthy individuals and patients
with head and neck carcinomas. Each peripheral blood sample was split into two portions, one for the establishment of a lymphoid
line and the other for short-term culture, which was used to estimate bleomycin sensitivity by cytogenetic procedures. Twenty
lymphoid lines were selected at random to compare bleomycin sensitivity with data obtained from short-term lymphocyte cultures.
In each set, bleomycin sensitivity of lymphoid cells was similar to that of the lymphocytes. The lymphoid lines, which can
be propagated for an unlimited supply of relatively homogeneous cellular material, will be useful for a variety of future
investigations.
This investigation was supported by grants from the John S. Dunn Foundation, Houston, TX, the Esther Knispel Fund administered
by The University of Texas M. D. Anderson Cancer Center, Houston, TX, and Department of Health and Human Services PHS grant
DE 07007. 相似文献
144.
Edward M. Mills Palur G. Gunasekar Goran Pavlakovic Gary E. Isom 《Journal of neurochemistry》1996,67(3):1039-1046
145.
Abstract: The relationship between iron-dependent fetal mouse spinal cord neuron injury and the generation of endogenous lipid hydroperoxides (LOOHs) has been investigated. Cultured spinal cord neurons were incubated with ferrous iron (3–200 µM). Cell viability was measured in terms of the uptake of α-[methyl-3H]aminoisobutyric acid ([3H]AIB). Both endogenously and iron-generated LOOH, i.e., free fatty acid hydroperoxide (FFAOOH), phosphatidylethanolamine hydroperoxide (PEOOH), and phosphatidylcholine hydroperoxide (PCOOH), were measured directly by an HPLC-chemiluminescence (HPLC-CL) assay. The FFAOOH, PEOOH, and PCOOH levels in neurons incubated with 200 µM Fe2+ for 40 min were, respectively, 22-, 158-, and sevenfold higher than those in non-iron-exposed cultures, demonstrating that phosphatidylethanolamine (PE) was most sensitive to peroxidation. The dose-response and time course of Fe2+-induced generation of these LOOHs were also established. In both experiments, the LOOH levels were correlated directly with loss of neuronal viability, suggesting strongly a direct relationship between lipid peroxidation and cell injury. On examination of the time course of the LOOH generation, an immediate increase in PEOOH and PCOOH levels with only 30 s of Fe2+ incubation was observed. In contrast, a lag phase in the increase in FFAOOH level (2 min after Fe2+ addition) suggested a delay in the activation of phospholipase A2 (PLA2) required for the hydrolysis and generation of FFAOOH. This culture system provides an excellent model for screening antioxidant neuroprotective compounds with regard to their ability to protect against iron-dependent peroxidative injury and the relationship of the neuroprotection to inhibition of lipid peroxidation and/or PLA2. 相似文献
146.
Kenneth G. Ross Edward L. Vargo Laurent Keller 《Evolution; international journal of organic evolution》1996,50(6):2387-2399
Variation in queen phenotype and reproductive role in the fire ant Solenopsis invicta has been shown to have a simple genetic basis in a single introduced population in the United States. The evidence consists of an association between this variation and queen genotype at Pgm-3, a phosphoglucomutase-encoding gene. In the present study, we surveyed Pgm-3 allele and genotype frequencies in diverse populations from the native and introduced ranges of this ant to learn whether this simple genetic basis for reproductive traits is a general feature of the species or a genetic anomaly in introduced ants stemming from a recent bottleneck or the invasion of novel habitats. No egg-laying queens living in polygyne (multiple-queen) nests possessed the homozygous genotype Pgm-3a/a in any of the study populations, yet nonreproductive females from such nests (workers as well as queens that had not yet initiated oogenesis) possessed this genotype at moderate frequencies. Remarkably, Pgm-3a/a was the most common genotype among all classes of females, including egg-laying queens, in monogyne (single-queen) nests from all populations studied. Genotype proportions at Pgm-3 in polygyne populations typically departed strongly from the proportions expected under Hardy-Weinberg equilibrium, whereas those in monogyne populations did not. These patterns establish that a single mendelian gene influences queen reproductive role in S. invicta and that this gene uniformly is under strong directional selection in the polygyne social form only. Moreover, the perfect association of Pgm-3 genotype and reproductive role in all populations, combined with the known function of phosphoglucomutase in insect metabolism, suggest that this gene may directly influence queen phenotypes rather than merely serving as a marker for a linked gene that causes the effects. 相似文献
147.
148.
Anthony B. Thompson Edward H. Allison Ben P. Ngatunga 《Environmental Biology of Fishes》1996,47(3):235-254
Synopsis Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km2, and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. bigeye, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the large Rhamphochromis group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices. 相似文献
149.
Edward L. Kean 《Glycoconjugate journal》1996,13(4):675-680
Mannosyl-P-dolichol (man-P-dol) has been shown to stimulate the early reactions of the dolichol pathway, specifically, the biosynthesis of GlcNAc-P-P-dol and GlcNAc-GlcNAc-P-P-dol, and thus may play a regulatory role in glycoprotein biosynthesis. The site of action of man-P-dol has previously been suggested to be the GlcNAc-transferase concerned with the formation of the monoglucosaminyl derivative. Since the concentration of the chitobiosyl compound also increases as a result of the presence of man-P-dol, the immediate site of the activation was reexamined. The effect of man-P-dol on the formation of GlcNAc-GlcNAc-P-P-dol using GlcNAc-P-P-dol synthesizedin situ or added exogenously as the substrate was investigated. In addition, the distribution of radioactivity in the glucosaminyl constituents of the products under the stimulatory conditions was determined. The results of these studies supported the conclusion that the stimulation of GlcNAc-lipid synthesis by man-P-dol is due to the enhanced synthesis of GlcNAc-P-P-dol. It is not a result of the activation of the GlcNAc-transferase catalyzing the attachment of the second GlcNAc residue for the biosynthesis of the chitobiosyl derivative.Abbreviations GlcNAc-P-P-dol
N-acetylglucosaminylpyrophosphoryldolichol
- GlcNAc-GlcNAc-P-P-dol
N-acetylglucosaminyl-N-acetylglucosaminylpyrophosphoryldolichol;
- chito
N-N-diacetylchitobiose
- man-P-dol
mannosylphosphoryldolichol
- TX-100
triton X-100
- Tes
2-{[tris-(hydroxymethyl)-methyl]-amino}-ethanesulfonic acid 相似文献
150.