全文获取类型
收费全文 | 2349篇 |
免费 | 136篇 |
专业分类
2485篇 |
出版年
2022年 | 13篇 |
2021年 | 23篇 |
2019年 | 13篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 50篇 |
2015年 | 56篇 |
2014年 | 57篇 |
2013年 | 185篇 |
2012年 | 118篇 |
2011年 | 121篇 |
2010年 | 78篇 |
2009年 | 66篇 |
2008年 | 135篇 |
2007年 | 122篇 |
2006年 | 116篇 |
2005年 | 129篇 |
2004年 | 140篇 |
2003年 | 129篇 |
2002年 | 130篇 |
2001年 | 43篇 |
2000年 | 40篇 |
1999年 | 36篇 |
1998年 | 38篇 |
1997年 | 22篇 |
1996年 | 34篇 |
1995年 | 17篇 |
1994年 | 26篇 |
1993年 | 18篇 |
1992年 | 32篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 16篇 |
1988年 | 29篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 27篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1975年 | 18篇 |
1974年 | 16篇 |
1972年 | 17篇 |
1968年 | 15篇 |
排序方式: 共有2485条查询结果,搜索用时 15 毫秒
21.
Y Kubota Y Watanabe H Otsuka T Tamiya T Tsuchiya J J Matsumoto 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1985,82(2):345-348
The antibacterial factor from the body surface of the African giant snail, Achatina fulica Férussac, was isolated by DEAE-Toyopearl 650M ion exchange chromatography. The isolated preparation exhibited highly positive antibacterial activity both for the Gram-positive bacteria, Bacillus subtilis and Staphylococcus aureus and for the Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, but it lost such activity when heated at 75 degrees C for 5 min. The antibacterial factor of the snail mucus was a glycoprotein whose molecular weight (MW) was about 160,000. It was composed of two subunits of MW 70,000-80,000. 相似文献
22.
23.
Mating behaviour ofTokunagayusurika akamusi searching at the resting place (lakeside vegetation, although mating also occurs in the air by swarming) was investigated
at the shore of Lake Biwa. Coinciding with the arrival of newly emerged adults, previously emerged males walked about to search
for mates at the resting place. When a searching male came into contact with a fresh (newly emerged) individual, he attempted
to copulate with it regardless of its sex. Consequently, males copulated with fresh females, which were more likely to be
virgin at the resting place, suggesting that the first male might contribute best to the fertilization. 相似文献
24.
Observations on the mating system of the midge,Tokunagayusurika akamusi, revealed mating to occur both in the air by swarming and on the ground by searching. At the shores of Lake Biwa, midges
appeared from November to early December. Newly emerged adults arrived at the resting place, lakeside vegetation, in the morning,
during which time a number of males also walked about in search of mates. Many copulating pairs were observed at the resting
place. Huge swarms occurred chiefly before sunset but the frequency of copulation observed in the swarm was extremely low.
It is likely that, in the Lake Biwa population, the proportion of females inseminated by searching males at the resting place
was much larger than that by swarming males in the air. Furthermore, by searching, males copulated with younger females than
by swarming. The differences between the searching and swarming tactics are discussed. 相似文献
25.
To analyze the boundaries of the functional coding region of the HSV-2(333) thymidine kinase gene (TK gene), deletion mutants of hybrid plasmid pMAR401 H2G, which contains the 17.5 kbp BglII-G fragment of HSV-2 DNA, were prepared and tested for capacity to transform LM(TK-) cells to the thymidine kinase-positive phenotype. These studies showed that hybrid plasmids containing 2.2-2.4 kbp subfragments of HSV-2 BglII-G DNA transformed LM(TK-) cells to the thymidine kinase-positive phenotype and suggested that the region critical for transformation might be less than 2 kbp. That the activity expressed in the transformants was HSV-2 thymidine kinase was shown by experiments with type-specific enzyme-inhibiting rabbit antisera and by disc-polyacrylamide gel electrophoresis analyses. DNA fragments of the HSV-2 TK gene were subcloned in phage M13mp9 and M13mp8. A sequence of 1656 bp containing the entire coding region of the TK gene and the flanking sequences was determined by the dideoxynucleotide chain termination method. Comparisons with the HSV-1(Cl 101) TK gene revealed that PstI, PvuII, and EcoRI cleavage sites had homologous locations as did promoter, translational start and stop, and polyadenylation signals. Extensive homology was observed in the nucleotide sequence preceding the ATG translational start signal and in portions of the coding region of the genes. Comparisons of the predicted amino acid sequences of the HSV-1 and HSV-2 thymidine kinase polypeptides revealed that both were enriched in alanine, arginine, glycine, leucine, and proline residues and that clear, but interrupted homology existed within several regions of the polypeptide chains. Stretches of 15-30 amino acid residues were identical in conserved regions. The possibility is suggested that domains containing some of the conserved amino acid sequences might have a role in substrate binding and as major antigenic determinants. 相似文献
26.
27.
Axial changes in the nemertean egg and embryo during development and its phylogenetic significance 总被引:4,自引:0,他引:4
On the basis of the axial relationship between the larva and adult, it is possible to divide the larvae of the members of the Heteronemertea and a species of the Palaeonemertea into five types, forming a sequential series in which the adult axis of each advances by an angle of 45° from that immediately preceding it. Phylogenetic consideration of the Nemertea has been undertaken in the light of evidence provided by the axiality of the embryos and the developmental data hitherto recorded. 相似文献
28.
29.
A Otsuka H Mikami T Tsunetoshi K Katahira A Moriguchi H Rakugi N Suzuki T Ogihara 《Biochemistry international》1990,22(2):353-359
Our previous study demonstrated that volume expansion with dextran produced blood pressure elevation due to vasoconstriction 3 hours after the cessation of infusion. To examine whether endogenous endothelin contributes to this vasoconstriction, we measured plasma level of endothelin before, immediately after, and 3 hours after the administration of dextran. Plasma level of endothelin decreased immediately after the administration (from 1.5 +/- 0.3 pg/ml to 1.1 +/- 0.2 pg/ml, P less than 0.05), and increased 3 hours after the administration (2.1 +/- 0.3 pg/ml, P less than 0.05). However, the changes in the plasma level of endothelin did not significantly correlated with those in blood pressure or total peripheral resistance. Thus, vasoconstriction after dextran infusion was accompanied by an increase in the plasma level of endothelin, but further evaluation is needed for the direct role of this peptide in the vasoconstrictive blood pressure elevation. 相似文献
30.