全文获取类型
收费全文 | 1451篇 |
免费 | 132篇 |
国内免费 | 1篇 |
出版年
2023年 | 12篇 |
2022年 | 13篇 |
2021年 | 31篇 |
2020年 | 26篇 |
2019年 | 26篇 |
2018年 | 38篇 |
2017年 | 26篇 |
2016年 | 46篇 |
2015年 | 64篇 |
2014年 | 66篇 |
2013年 | 75篇 |
2012年 | 108篇 |
2011年 | 102篇 |
2010年 | 51篇 |
2009年 | 52篇 |
2008年 | 62篇 |
2007年 | 69篇 |
2006年 | 68篇 |
2005年 | 53篇 |
2004年 | 60篇 |
2003年 | 35篇 |
2002年 | 38篇 |
2001年 | 34篇 |
2000年 | 33篇 |
1999年 | 20篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 28篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 22篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1975年 | 11篇 |
1972年 | 9篇 |
1970年 | 13篇 |
1966年 | 9篇 |
1965年 | 7篇 |
排序方式: 共有1584条查询结果,搜索用时 13 毫秒
21.
22.
23.
The study of an effect of exogenous thymidine on the mitotic cycle demonstrated that a 30 minute exposure to unlabeled and to tritiated thymidine at a concentration of 2.9 × 10?6 M was sufficient to cause a significant increase in the mitotic index of root meristem cells of Haplopappus gracilis. An analysis of the data revealed that this was due to the prolongation of metaphase rather than to an increase in the actual number of cells entering division. 相似文献
24.
25.
A biosynthetic method for preparing 35S-labelled lipoic acid 总被引:1,自引:0,他引:1
26.
Summary A new variety of Gloeocapsa, G. crepidinum Thuret var. ghazipurensis n. var., has been isolated from enrichment cultures of paddy field soils of Ghazipur, Uttar Pradesh, India. The alga has been studied in detail. The form is especially interesting since it showed certain growth-stages recorded in G. alpina Naeg.The authors are thankful to Rev. Dr. H. Santapau for rendering the Latin diagnosis of the new variety. 相似文献
27.
J Mitra N R Prabhakar J L Overholt N S Cherniack 《Journal of applied physiology》1989,67(5):1814-1819
We studied the central effects of N-methyl-D-aspartate (NMDA) on respiration in 18 artificially ventilated cats anesthetized with alpha-chloralose. Unilateral topical application of NMDA (1 x 10(-8) mol) to the intermediate region of the ventrolateral medulla exaggerates the phrenic response to CO2 at end-tidal PCO2 levels of less than 50.0 Torr. At higher end-tidal PCO2 levels, however, such differences disappear. Unilateral NMDA application increases the activity of the right and left phrenic nerves equally. Furthermore, the magnitude of the phrenic response after unilateral application of NMDA was not different from that after bilateral application. NMDA also had a vasopressor action when applied to the ventrolateral medullary surface. In contrast to respiratory responses, bilateral application of NMDA caused a significant increase in blood pressure compared with unilateral application of NMDA. Application of the NMDA antagonist 2-amino-5-phosphonovaleric acid abolished both the blood pressure and respiratory effects of NMDA. These results suggest that CO2 and NMDA may act on a common respiratory premotoneuron to produce stimulation of breathing. Because blood pressure responses, unlike respiratory responses, were greater after bilateral application than after unilateral application of NMDA, it is suggested that the neural substrates for the two effects of NMDA seem to be different. 相似文献
28.
29.
The crystal structure of a dipeptide L -leucyl–L -leucine (C12H24N2O3) has been determined. The crystals are monoclinic, space group P21, with a = 5.434(4) Å, b = 15.712(7) Å, c = 11.275(2) Å, β = 100.41(1)°, and Z = 2. The crystals contain one molecule of dimethyl sulfoxide (DMSO) as solvent of crystallization for each dipeptide molecule. The structure has been solved by direct methods and refined to a final R index of 0.059 for 920 reflections (sinθ/λ ? 0.60 Å?1) with I ? 2σ (I). The trans peptide unit shows substantial degree of non-planarity (Δω = 14°). The peptide backbone adopts an extended conformation with torsion angles of ψ1 = 138(1)°, ω1 = 166(1)°, ?2 = ? 149.3(7)°, ψ21 = 164.2(7)°, and ψ22 = ? 15(1)°. For the first leucyl residue, the side-chain conformation is specified by the torsion angles 1χ1 = 176.7(7)°, 1χ21 = 62(1)°, 1χ22 = ? 177.4(8)°; the second leucyl residue adopts a Sterically unfavorable conformation with 2χ1 = 61(1)°, 2χ21 = 97(1)°, and 2χ22 = ?151(1)°. The packing involves head-to-tail interaction of peptide molecules and segregation of polar and nonpolar regions. The DMSO molecule is strongly hydrogen bonded to the terminal NH group. © 1994 John Wiley & Sons, Inc. 相似文献
30.
Antisera towards neurotensin (NT) and the structurally related peptide, LANT6, were used to characterize immunoreactive peptides and proteins in extracts of chicken tissues. A 17 kDa protein was identified by Western blotting as a potential precursor to NT and LANT6. However, the posttranslational processing of this common precursor appeared to be tissue specific, giving rise to disproportionate amounts of NT and LANT6, along with varying expression of a large molecular LANT6 (Mr, 15 kDa). The intestinal cells containing immunoreactive NT, LANT6, and large molecular LANT6 behaved similarly during fractionation by size and density. These activities also banded together in particles resembling vesicles during centrifugation of isotonic homogenates of tissue. These results suggest that chicken NT and LANT6 are biosynthesized as parts of the same precursor, the processing of which can give rise to a variety of products stored within secretory vesicles. 相似文献