全文获取类型
收费全文 | 280245篇 |
免费 | 14959篇 |
国内免费 | 860篇 |
出版年
2018年 | 13575篇 |
2017年 | 12359篇 |
2016年 | 9745篇 |
2015年 | 2929篇 |
2014年 | 3447篇 |
2013年 | 4808篇 |
2012年 | 9283篇 |
2011年 | 18242篇 |
2010年 | 15708篇 |
2009年 | 11624篇 |
2008年 | 14737篇 |
2007年 | 16523篇 |
2006年 | 5345篇 |
2005年 | 5252篇 |
2004年 | 5877篇 |
2003年 | 5812篇 |
2002年 | 5526篇 |
2001年 | 8789篇 |
2000年 | 8887篇 |
1999年 | 6471篇 |
1998年 | 2092篇 |
1997年 | 2134篇 |
1996年 | 1877篇 |
1993年 | 1762篇 |
1992年 | 5311篇 |
1991年 | 5485篇 |
1990年 | 5252篇 |
1989年 | 5213篇 |
1988年 | 4842篇 |
1987年 | 4576篇 |
1986年 | 4160篇 |
1985年 | 4322篇 |
1984年 | 3510篇 |
1983年 | 3000篇 |
1982年 | 2007篇 |
1981年 | 1808篇 |
1980年 | 1784篇 |
1979年 | 3311篇 |
1978年 | 2625篇 |
1977年 | 2373篇 |
1976年 | 2151篇 |
1975年 | 2652篇 |
1974年 | 2984篇 |
1973年 | 2903篇 |
1972年 | 2988篇 |
1971年 | 2761篇 |
1970年 | 2216篇 |
1969年 | 2137篇 |
1968年 | 1985篇 |
1967年 | 1832篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
151.
A procedure for the stimulation of axillary bud developmentfrom young shoots of maize, their subculture to root-inducingmedia and transfer as rooted plants to soil is described. Axillarybud development was enhanced by the addition of kinetin andauxin to the culture medium. Root initiation on explanted axillarybuds, while successful with some cultivars, was variable. Anumber of mature plants with normal tassels and ears were producedfrom the lowermost buds of an original stem explant. Buds fromhigher positions on the explant exhibited different potentialitieswith some, those normally from cob producing nodes, producingshort-stalked plants with terminal female influorescences. Agradient of bud potentiality along the stem appears to be establishedextremely early after each is initiated. Zea mays., corn, maize, shoot tip culture, clone, vegetative propagation 相似文献
152.
A particularly vexing phenomenon within invasion ecology is the occurrence of spontaneous collapses within seemingly well-established exotic populations. Here, we assess the frequency of collapses among 68 exotic bird populations established in Hawaii, Puerto Rico, Los Angeles and Miami. Following other published definitions, we define a ‘collapse’ as a decline in abundance of ≥90 % within ≤10 years that lasts for at least 3 years. We show that 44 of the 68 exotic bird populations have exhibited declines at some point within their time series. Sixteen of the populations declined sufficiently to be defined as collapsed. It took on average 3.8 ± 1.8 years for populations to decline into a collapsed state, and this state persisted on average for 7.1 ± 6.3 years across (collapsed) populations. We compared the severity and duration of declines across all 44 declining populations according to taxonomic Order and geographic region. Neither variable explained substantial variation in the metrics of collapse. Our results indicate that severe, rapid, and persistent population declines may be common among exotic populations. We suggest that incorporating the probability and persistence of collapses into management decisions can inform efforts to enact control or eradication measures. We also suggest that applying our approach to other taxa and locations is crucial for improving our understanding of when and where collapses are likely to occur. 相似文献
153.
I. Grebenščikov E. Hoffmann P. Metzner F. Mechelke K. Mothes A. Bail 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1953,23(1-2):61-63
Ohne Zusammenfassung 相似文献
154.
155.
E. B. Burova I. S. Smirnova A. N. Shatrova I. V. Gonchar N. N. Nikolskii 《Cell and Tissue Biology》2011,5(1):9-14
Interferon gamma (IFNγ) is known to inhibit the proliferation of some transformed cell lines. Recently, we demonstrated the
transactivation of the epidermal growth factor receptor (EGFR) in response to IFNγ (Burova et al., 2007) and provided direct
evidence for the dependence of IFNγ-induced EGFR transactivation on the EGFR expression level in epithelial cells (Gonchar
et al., 2008). This study examines an antiproliferative effect of IFNγ on human epithelial cell lines—A431 and HeLa that express
high levels of EGFR, as well as HEK293 that expresses low levels of EGFR. To characterize the IFNγ-induced changes in these
cells, we studied cell growth, the cell cycle, and induction of apoptosis. The response to IFNγ differed in the compared cell
lines; cell growth was inhibited in both A431 and HeLa cells, but not in HEK293 cells, as was shown by the cell count and
MTT. The cell-cycle phases analyzed by flow cytometry were disturbed in A431 and HeLa cells in response to IFNγ. On the contrary,
in HEK293 cells, the IFNγ treatment did not alter distribution by cell cycle phases. Our results indicate that IFNγ produces
an antiproliferative effect that depends on the increased expression of EGFR in A431 and HeLa cells. Furthermore, it was demonstrated
that IFNγ induced the caspase 3 activation in A431 cells, which suggests the involvement of active caspase 3 in the IFNγ-induced
apoptosis. 相似文献
156.
157.
158.
159.
160.
S. T. Zakhidov T. L. Marshak E. A. Malolina A. Yu. Kulibin I.A. Zelenina S. M. Pavluchenkova V. M. Rudoi O. V. Dement’eva S. G. Skuridin Yu. M. Evdokimov 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(3):293-296
The effect of gold nanoparticles on mouse epididymal sperm has been studied using the model system of nuclear chromatin decondensation
in vitro. It is shown that the treatment of gametes, preliminary membrane-freed by sodium dodecyl sulfate, in the mediums
containing gold nanoparticles (with diameter ∼2.5 nm) in concentrations 1.0 × 1015 or 0.5 × 1015 particles/ml and following incubation in dithiothreitol solution (DTT) resulted in failure of chromatin decondensation process
and nucleus structure. We conclude that gold nanoparticles possess spermatotoxicity. The mechanism of cytotoxic effect of
gold nanoparticles may be related with their interaction with molecules of double-helix DNA. The model system studied in this
research is applicable for further investigations of cytotoxic effects of nanoparticles of different origin and made of different
metals. 相似文献