全文获取类型
收费全文 | 110478篇 |
免费 | 13261篇 |
国内免费 | 412篇 |
出版年
2018年 | 990篇 |
2017年 | 964篇 |
2016年 | 1257篇 |
2015年 | 1550篇 |
2014年 | 1942篇 |
2013年 | 2461篇 |
2012年 | 2860篇 |
2011年 | 2809篇 |
2010年 | 1885篇 |
2009年 | 1845篇 |
2008年 | 2358篇 |
2007年 | 2343篇 |
2006年 | 2332篇 |
2005年 | 2133篇 |
2004年 | 2070篇 |
2003年 | 2103篇 |
2002年 | 2073篇 |
2001年 | 9640篇 |
2000年 | 9509篇 |
1999年 | 7195篇 |
1998年 | 1614篇 |
1997年 | 1792篇 |
1996年 | 1580篇 |
1995年 | 1407篇 |
1994年 | 1308篇 |
1993年 | 1249篇 |
1992年 | 4792篇 |
1991年 | 4522篇 |
1990年 | 3992篇 |
1989年 | 4012篇 |
1988年 | 3608篇 |
1987年 | 3084篇 |
1986年 | 2776篇 |
1985年 | 2678篇 |
1984年 | 1973篇 |
1983年 | 1729篇 |
1982年 | 1230篇 |
1981年 | 983篇 |
1980年 | 913篇 |
1979年 | 1762篇 |
1978年 | 1361篇 |
1977年 | 1199篇 |
1976年 | 1028篇 |
1975年 | 1149篇 |
1974年 | 1166篇 |
1973年 | 1162篇 |
1972年 | 1033篇 |
1971年 | 955篇 |
1970年 | 822篇 |
1969年 | 743篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
W Nakamura Y Nagano K Otsuka Y Nishimoto 《Comptes rendus des séances de la Société de biologie et de ses filiales》1980,174(1):104-107
The interferon inducing effect of hyperthermia was studied in normal and tumor-bearing mice. Circulating interferon was temporarily detected one day after subcutaneous transplantation of 1.6 X 10(6) Ehrlich's ascites tumor cells. Hyperthermia of 43.5 degrees C for 5 min did not induce the interferon formation in mice with or without subcutaneous tumor of the cells. These findings showed that the induction of interferon formation was not main cause of the hyperthermia-induced tumor inhibition. 相似文献
202.
J. Yamaguchi S. Itoh T. Saitoh A. Ikeda T. Tashiro Y. Nagato 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,98(1):32-38
β-Amylase deficiency in various cultivars of rice was examined at the molecular level. Using an antibody against β-amylase
purified from germinating seeds of rice, we were able to demonstrate the expression and organization of the β-amylase gene
in normal and deficient cultivars. Although β-amylase is a starch-hydrolyzing enzyme, as is α-amylase, the β-amylase protein/gene
is expressed differently from the α-amylase protein/gene; i.e. (1) β-amylase is synthesized only in aleurone cells, (2) the
enzyme production in the embryo-less half-seeds is not under hormonal control. We identified some cultivars of rice that are
deficient for β-amylase activity. We present new evidence that synthesis is blocked at the level of mRNA synthesis in the
deficient cultivars. The usefulness of β-amylase as a crop trait is also discussed.
Received: 8 May 1998 / Accepted: 5 June 1998 相似文献
203.
204.
Current patterns of floral design in Pedicularis must have undergone an evolutionary process of interacting among components of floral traits, and then formed internal relationships among these traits. To detect such correlations, which may provide insight to understand flower evolution, 40 Pedicularis species representing all corolla types of the genus were studied. Results show that, interspecifically, pollen size correlates negatively with pollen number, but positively with pistil length. This suggests that plants evolve an optimal pollen size, which balances the advantages of large pollen size for gametophytic competition against the fecundity disadvantages of fewer pollen grains. In contrast to sex allocation theory, this study does not find a trade-off, but an interspecific positive correlation between pollen and ovule number. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the lack of negative correlation between male and female function.This work was supported by the State Key Basic Research and Development Plan, China (Grant No. G2000046804) to YHG. The authors would like to thank Peter K. Endress and two anonymous reviewers for providing critical comments and helpful suggestions, Qing-Feng Wang, Jing-Yuan Wang and Jin-Ming Chen for their helpful suggestions. Shi-Guo Sun, Jing Xia, and Qian Yu are thanked for their assistance in both the field work and laboratory phases of the project. 相似文献
205.
206.
207.
208.
The effect of one massive dose of cytoxan (150 mg/kg), as an alkylating agent, on the morphology of sarcoma 180 cells was followed after 1, 3, 6, 12, 24, 48, 96, 120, and 168 h. After 1 h the cells of treated tumour showed clumping and a decrease in their size. In addition, statistical analysis manifested significant decrease in all phases of mitotic figures. All mitotic figures were completely stopped after 3 h from cytoxan treatment. After 6 and 12 h from cytoxan treatment the hyaline degenerations became more marked in the treated tumour tissue. Chromosomal bridge formation, nuclei aberrations and polynuclear cells were more prominent in 24, 48, and 96 h from cytoxan treatment. Increase in the nuclear size and hyaline degeneration were observed in treated section of 120 and 168 h. 相似文献
209.
N Nakagata K Matsumoto M Anzai A Takahashi Y Takahashi Y Matsuzaki K Miyata 《Jikken dobutsu》1992,41(4):537-540
Spermatozoa of a homozygous transgenic mouse, in which the firefly luciferase gene was expressed under the control of beta-actin promoter, were frozen at -196 degrees C. One fourth of the frozen sperm was later thawed and used for in vitro fertilization. Thirty-six of 65 oocytes (55.4%) developed to the 2-cell stage. All the 2-cell embryos were transferred to the oviducts of pseudopregnant recipients and 23 young (63.9%, 23/36) were born. All of young analyzed carried the transgene and showed the luciferase gene expression. 相似文献
210.
A tertiary structure prediction is described using Monte Carlo simulated annealing for the peptide fragment corresponding to residues 16-36 of bovine pancreatic trypsin inhibitor (BPTI). The simulation starts with randomly chosen initial conformations and is performed without imposing experimental constraints using energy functions given for generic interatomic interactions. Out of 20 simulation trials, seven conformations show a sheet-like structure--two strands connected by a turn--although this sheet-like structure is not as rigid as that observed in native BPTI. It is also shown that these conformations are mostly looped and exhibit a native-like right-handed twist. Unlike the case with the C-peptide of RNase A, no conspicuous alpha-helical structure is found in any of the final conformations obtained in the simulation. However, the lowest-energy conformation does not resemble exactly the native structure. This indicates that the rigid beta-sheet conformation of native BPTI merely corresponds to a local minimum of the energy function if the fragment with residues 16-36 is isolated from the native protein. A statistical analysis of all 20 final conformations suggests that the tendency for the peptide segments to form extended beta-strands is strong for those with residues 18-24, and moderate for those with residues 30-35. The segment of residues 25-29 does not tend to form any definite structure. In native BPTI, the former segments are involved in the beta-sheet and the latter in the turn. A folding scenario is also speculated from this analysis. 相似文献