全文获取类型
收费全文 | 5160篇 |
免费 | 296篇 |
国内免费 | 956篇 |
出版年
2024年 | 22篇 |
2023年 | 79篇 |
2022年 | 142篇 |
2021年 | 147篇 |
2020年 | 120篇 |
2019年 | 172篇 |
2018年 | 219篇 |
2017年 | 129篇 |
2016年 | 159篇 |
2015年 | 164篇 |
2014年 | 414篇 |
2013年 | 482篇 |
2012年 | 298篇 |
2011年 | 289篇 |
2010年 | 265篇 |
2009年 | 291篇 |
2008年 | 324篇 |
2007年 | 381篇 |
2006年 | 268篇 |
2005年 | 294篇 |
2004年 | 216篇 |
2003年 | 207篇 |
2002年 | 191篇 |
2001年 | 144篇 |
2000年 | 125篇 |
1999年 | 114篇 |
1998年 | 97篇 |
1997年 | 68篇 |
1996年 | 75篇 |
1995年 | 62篇 |
1994年 | 63篇 |
1993年 | 49篇 |
1992年 | 29篇 |
1991年 | 41篇 |
1990年 | 36篇 |
1989年 | 31篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1972年 | 4篇 |
排序方式: 共有6412条查询结果,搜索用时 15 毫秒
91.
The reduction of cytochrome c by beef liver sulfite oxidase was found to be strongly inhibited by high ionic strength, indicating the importance of electrostatic interactions to the reaction. The reaction rates of sulfite oxidase with singly trifluoroacetylated or trifluoromethylphenylcarbamylated cytochrome c derivatives were studied to determine the role of individual lysines in the reaction. The reaction rate was decreased by modification of the lysines immediately surrounding the heme crevice, the decreases following the order: Lys 13 > Lys 25 Lys 79 ≈ Lys 87 > Lys 8 ≈ Lys 27 ≈ Lys 72. Modification of lysines 22, 55, 88, 99, and 100 had no effect on the reaction rate. These results indicate that the interaction site on cytochrome c for sulfite oxidase is at the heme crevice region, and overlaps considerable with that for cytochrome oxidase. 相似文献
92.
Summary Parts of the Wulst region of the chick embryo brain were maintained for 39 days in vitro. Processes of adjacent glial cell form zonulae occludentes and desmosomal junctions in the uppermost stratum of the cultures. Subjacent to this layer, in the neuropil, axodendritic synapses are abundant. 10–20 m below the surface the perikarya of glial cells and neurons are found. The latter form small clusters, plasma membranes of contiguous cells being directly apposed to each other. Axosomatic synapses terminate on the perikarya. Occasionally one terminal synapses on two nerve cells simultaneously. Two types of cilia arise from basal bodies in the cytoplasm of nerve cells. Type I is a slender protrusion of about 0.5 m in diameter, extending into the neuropil. On transverse sections it displays a 9 + 0 pattern of organization of paired micro tubules proximally, and an 8 + 1 configuration more distally. The length of the cilium is approximately 7 m. Type II cilia also originate in the neuronal cytoplasm. The structure of the proximal portion is identical with that of type I cilia. Toward the tip, however, the type II cilium is characterized by a bulbous enlargement which is filled with loosely folded membranes. The fine structural details of this cilium correlate closely to the outer segments of retinal photoreceptor cells during differentiation. The possible role of a light receptor in the Wulst region of birds, controlling biological rhythms, is discussed.
Acknowledgements. The authors wish to thank Mrs. H. Frenk for her expert assistance in tissue culture and electron microscopic techniques 相似文献
93.
94.
95.
深圳市西海岸和海域生物资源多样性的管护 总被引:3,自引:0,他引:3
王献溥 《植物资源与环境学报》1992,1(1):1-5
本文着重介绍生物多样性管护区的基本含义和要求,结合深圳市西海岸和海域的特点,提出建立珠江口南海海岸和海洋生物多样性管护区,以发挥该区域的资源优势和持续利用,为建设深圳特区做出应有的贡献。 相似文献
96.
Tokuo Ogawa Junichi Sugenoya Norikazu Ohnishi Keiko Natsume Megumi Ochiai Motohiko Nishida Norihiko Shinoda Kenichi Katoh Ritsuko Imamura 《International journal of biometeorology》1991,35(1):18-23
In an attempt to detect differences in the thermal effect of infrared irradiation of different wavelengths, transient sweating response to infrared irradiation in various spectral regions was examined. In Series 1, the ventral or dorsal surface of the nude subject was irradiated repetitively for a period of 4 min (2 min on, 2 min off) by each of three kinds of infrared heaters with main emissivity in near-infrared (NIR; 0.7–2.8 m), intermediate-infrared (MIR; 1.5–5.8 m), and far-infrared (FIR; 2.8–25 m) regions. The sweating response on a non-irradiated area tended to be the greatest with MIR, while the magnitude of the sweating response on the irradiated area showed no consistent differences among various wavelengths. The results infer that MIR stimulated cutaneous thomoreceptors most effectively, while its direct effect on local sweat gland activity was minimal. In Series 2, the effects of 9–12 min irradiations in more restricted ranges of wavelength were compared by the combination of the three kinds of heaters with filters (translucent to wavelength ranges of 1.3–2.7, 2.7–3.5, 3.6–8.0 m, respectively). The sweating response on a remote area was predominantly greater with the range of 2.7–3.5 m than with the other wavelength ranges, while the local effect on sweating was minimal with this range. The results of Series 2 reinforce those of Series 1, indicating that the degree of stimulation of cutaneous thermoreceptors and of direct thermal effect on sweat gland activity differ with spectral regions incident on the skin, thus affecting local and remote effects on the sweating response. 相似文献
97.
黄土丘陵半干旱区不同作物生态效能研究 总被引:5,自引:0,他引:5
深入研究特定生态环境条件下不同作物生产力及其生态效能,对于合理调控农田生态系统,探讨提高系统生产力途径具有重要意义。60年代以来,在国际生物学计划(IBP)的影响下,美国、日本、菲葎宾等国先后进行了小麦、水稻、大豆等作物农田生态效能研究。我国于“六·五”期间分别在南方稻区、黄淮海平原以及北方灌区等不同农业区开展了多种作物种植制度生产力问题研究,并取得重 相似文献
98.
Bayesian analyses for a multiple capture-recapture model 总被引:3,自引:0,他引:3
99.
100.
A simple method for shortening a plasmid genome using a system of plasmid cointegration mediated by a Tn3 mutant 总被引:3,自引:0,他引:3
This paper describes a simple method for the isolation of small plasmids of various sizes from pSMI, a derivative of the resistance plasmid R 100. The method is based on the observation that a repressor-negative mutant of the ampicillin-resistance (ampr) transposon Tn3, Tn3 No. 5, mediates cointegration of a plasmid carrying Tn 3 No. 5 (pMB8::Tn 3 No. 5) into virtually any site on pSMI. The resulting cointegrate plasmids contain the pSMI sequence which is joined with the ampr gene of the Tn 3 mutant. This cointegration is so frequent that large cointegrate plasmids can be readily detected in the total plasmid DNA prepared from cells carrying pSMI and pMB8::Tn3 No. 5. We were able to isolate small plasmids of various sizes by digesting the total plasmid DNAs with restriction endonucleases which cut both pSM 1 and Tn3 No. 5 sequences present in the cointegrates and subsequently ligating the restriction fragment containing both the ampr gene and the region necessary for replication of pSMI. Analysis of these plasmids, named pBV plasmids, with restriction endonucleases and by nucleotide sequencing allowed us to determine regions necessary or unnecessary for replication, thus defining a minimal replication region of pSMI. The present method is generally useful for the isolation of small derivatives from any large plasmid for the study of genes and sites adjacent to or within the minimal replication region of the plasmid. 相似文献