全文获取类型
收费全文 | 4788篇 |
免费 | 380篇 |
国内免费 | 2篇 |
出版年
2023年 | 33篇 |
2022年 | 31篇 |
2021年 | 81篇 |
2020年 | 42篇 |
2019年 | 41篇 |
2018年 | 99篇 |
2017年 | 102篇 |
2016年 | 124篇 |
2015年 | 182篇 |
2014年 | 221篇 |
2013年 | 289篇 |
2012年 | 355篇 |
2011年 | 331篇 |
2010年 | 222篇 |
2009年 | 195篇 |
2008年 | 282篇 |
2007年 | 291篇 |
2006年 | 244篇 |
2005年 | 245篇 |
2004年 | 250篇 |
2003年 | 232篇 |
2002年 | 222篇 |
2001年 | 103篇 |
2000年 | 109篇 |
1999年 | 83篇 |
1998年 | 64篇 |
1997年 | 36篇 |
1996年 | 54篇 |
1995年 | 29篇 |
1994年 | 38篇 |
1993年 | 21篇 |
1992年 | 46篇 |
1991年 | 45篇 |
1990年 | 37篇 |
1989年 | 33篇 |
1988年 | 31篇 |
1987年 | 17篇 |
1986年 | 25篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 27篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 23篇 |
1975年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有5170条查询结果,搜索用时 15 毫秒
81.
Cyclopiazonic acid is a toxic metabolite of fungal origin that inhibits protein synthesis in intact HeLa cells and eukaryotic cell-free systems. It has been shown that cyclopiazonic acid blocks the GTP- and EF-1-dependent binding of (3H)Phe-tRNA to 80S ribosomes. Moreover the translocation of N-Ac-(3H)Phe-tRNA by 80S ribosomes that takes place in the presence of EF-2 and GTP is also halted by cyclopiazonic acid. It is concluded that this drug affects a ribosomal site involved in the alternative interaction of elongation factors EF-1 and EF-2. 相似文献
82.
83.
A new homeobox-leucine zipper gene from Arabidopsis thaliana 总被引:3,自引:0,他引:3
Jim Mattsson Eva Söderman Marie Svenson Chumpol Borkird Peter Engström 《Plant molecular biology》1992,18(5):1019-1022
We have isolated a homeobox-containing gene from Arabidopsis thaliana using a degenerate oligonucleotide probe corresponding to the most conserved region of the homeodomain. This strategy has been used previously to isolate homeobox-containing genes from Caenorhabditis, and recently from A. thaliana. The Arabidopsis genes have an unusual structure in that they have a leucine zipper motif adjacent to the carboxy terminal region of the homeo domain, a feature not found in homeobox-containing genes isolated from animals. We report the isolation and primary structure of a new member of this Arabidopsis homeobox-leucine zipper gene family. This new member has the homeodomain and leucine-zipper motif similar to the two genes previously identified, but differs from these genes in the part corresponding to the carboxy terminus of the polypeptide, as well as in size and isoelectric point of the protein. 相似文献
84.
85.
The photosynthesis of Dunaliella parva Lerche as a function of temperature,light and salinity 总被引:1,自引:0,他引:1
The photosynthetic behaviour of Dunaliella parva Lerche from the athalassic lagoon of Fuente de Piedra (Málaga, Southern Spain) was studied experimentally at three NaCl concentrations (1, 2 and 3 M), five temperatures (15, 23, 31, 38 and 42°C) and nine different irradiances between 82 and 891 mol m–2 s–1. Results are analyzed to define the best growing conditions for the algae.
D. parva shows the highest photosynthetic rates at a NaCl molarity of 2 M, under a moderate light intensity (600 mol m–2 s–1) at 31°C. Above this light intensity a clear photoinhibition of the photosynthesis was found at 2 M and 3 M of NaCl. D. parva is a halotolerant and a thermoresistant species as evidenced by its net photosynthesis rate and positive values of oxygen evolution at 42°C.Two methods for modelling photosynthesis vs. irradiance curves are discussed. The first is a single model, based on third-order polynomial equations, and the second is double model, based on hyperbolical Michaelis-Menten type functions and negative exponential to define photoinhibition. 相似文献
86.
Jim Hardie 《Journal of insect physiology》1981,27(5):347-355
Long days (short nights) (LD 16:8) and high temperatures (> 15°C) have an apterizing effect on the short day (LD 12:12) induced, presumptive gynopara of Aphis fabae. Transfer of presumptive gynoparae to long days (15°C) or to 25°C (short days) at varying times during postnatal development demonstrate that the adult form is determined by the second day of the second instar, i.e. 5 days after birth at 15°C. Transfer on day 1 induces maximum apterization with the proportion of aphids affected decreasing with age at transfer.Apterization induced by long days immediately after birth can, to some extent, be cancelled by return to short days but only up to day 4. Thus long days are morphogenetically more potent than short days at the beginning of larval development. At temperatures above 15°C the proportion of aphids apterized increases almost linearly.Apterized insects can be distinguished from juvenilized insects in the fifth-instar. Topical application of juvenile hormone (JH) induces both apterization and juvenilization of presumptive gynoparae but at different times during larval development, JH treatment during the early-instars promotes apterization but induces little juvenilization, whereas maximum juvenilization, without apterization, is produced by middle-instar treatment. The apterizing effects of JH are, thus, not due to its neotenic action.The response profile of JH-induced apterization is similar to that observed with long days and 25°C. It is suggested that such conditions increase endogenous JH levels in A. fabae. The three naturally occurring JH's differ in activity in the order JH I > JH II > JH III. Both long-day and JH-apterized insects switch from the normal ovipara production of the adult gynopara to vivipara production. 相似文献
87.
Survival of Paracoccidioides brasiliensis yeast cells under microaerophilic conditions 总被引:1,自引:0,他引:1
The ability of P. brasiliensis yeast cells to withstand microaerophilic conditions was investigated in a liquid medium distributed in tall columns in screw-capped tubes. Young cells of three isolates were inoculated on top of the medium, and the tubes were incubated aerobically and anaerobically at 36 degrees C for 28 days. The viability of cells that had sedimented to the bottoms of the tubes was studied by fluorescent microscopy and by their capacity to resume growth when transferred to fresh medium under continuous agitation. The proportion of viable cells in the sediments diminished with time of incubation. However, after 28 days, 27% of the cells were still viable and fully capable of active growth when placed under adequate aeration. On the other hand, drastic reduction of oxygen access elicited an accelerated death rate, with no survival after 7 days of incubation. 相似文献
88.
Experiments with anesthetized cats were done to study possible roles of different prostaglandins (PGs) in modulating sympathetic neuroeffector transmission. We recorded contractions of the nictitating membrane (n.m.), blood flow in the carotid artery, heart rate and blood pressure, both under control conditions and while stimulating the cut cervical sympathetic nerve. Intra-carotid arterial injection (i.a.) of PGD2 depressed sympathetic transmission to the n.m. without depressing the effects of exogenous norepinephrine (NE). In contrast, PGE2 enhanced the effects of nerve transmission or exogenous NE on the stimulated n.m. PGI2 had similar but shorter effects to PGE2. PGF2α or a stable PGH2 analog, contracted the n.m. smooth muscle with no detected effect on nerve transmission. Carotid blood flow was increased by PGD2, PGE2 and PGI2. PGD2 and PGI2 caused bradycardia that could be blocked by atropine. This ability of PGD2 to modulate autonomic nerve activity is of particular interest because of recent reports that nerve tissue synthesizes PGD2. 相似文献
89.
O.V. Miller J.W. Aiken R.J. Shebuski R.R. Gorman 《Prostaglandins & other lipid mediators》1980,20(2):391-400
A direct comparison of the relative potencies of the two anti-aggregatory prostaglandins PGI2 and 6-keto-PGE1 showed PGI2 was at least 20 times more potent than 6-keto-PGE1 when tested against ADP-induced human platelet aggregation. This marked difference in potency was even more evident when the ability of PGI2 and 6-keto-PGE1 to stimulate platelet cyclic AMP levels was determined. When cyclic AMP levels were measured direct comparisons were difficult because the respective dose response curves were not parallel, but 10 ng of PGI2 was equivalent to 300 ng of 6-keto-PGE1.PGI2 was also more potent (10–20 times) than 6-keto-PGE1 as a disaggregatory agent, and the disaggregatory activity of both prostaglandins was enhanced by the phosphodiesterase inhibitor 1-methyl-3-isobutylmethylxanthine.PGI2 was also more active than 6-keto-PGE1 as an inhibitor of thrombus formation in dog coronary arteries in vivo. In vivo, 6-keto-PGE1 was at least 10 times less potent than PGI2, the exact difference could not be determined because 6-keto-PGE1 caused significant falls in blood pressure before anti-platelet activity could be detected.PGI2 is an intrinsically more potent anti-aggregatory molecule than 6-keto-PGE1, but these data do not rule out the possibility that some of the activities attributed to PGI2 could be the result of the conversion of PGI2 and/or 6-keto-PGF1α to 6-keto-PGE1. 相似文献
90.