全文获取类型
收费全文 | 17373篇 |
免费 | 46篇 |
国内免费 | 60篇 |
专业分类
系统科学 | 259篇 |
丛书文集 | 444篇 |
教育与普及 | 36篇 |
理论与方法论 | 51篇 |
现状及发展 | 7982篇 |
研究方法 | 735篇 |
综合类 | 7823篇 |
自然研究 | 149篇 |
出版年
2012年 | 214篇 |
2011年 | 413篇 |
2010年 | 103篇 |
2009年 | 95篇 |
2008年 | 280篇 |
2007年 | 349篇 |
2006年 | 301篇 |
2005年 | 306篇 |
2004年 | 275篇 |
2003年 | 328篇 |
2002年 | 264篇 |
2001年 | 611篇 |
2000年 | 615篇 |
1999年 | 344篇 |
1993年 | 87篇 |
1992年 | 328篇 |
1991年 | 254篇 |
1990年 | 301篇 |
1989年 | 278篇 |
1988年 | 263篇 |
1987年 | 280篇 |
1986年 | 286篇 |
1985年 | 338篇 |
1984年 | 242篇 |
1983年 | 221篇 |
1982年 | 201篇 |
1981年 | 239篇 |
1980年 | 261篇 |
1979年 | 571篇 |
1978年 | 465篇 |
1977年 | 470篇 |
1976年 | 352篇 |
1975年 | 375篇 |
1974年 | 586篇 |
1973年 | 458篇 |
1972年 | 419篇 |
1971年 | 511篇 |
1970年 | 657篇 |
1969年 | 573篇 |
1968年 | 493篇 |
1967年 | 529篇 |
1966年 | 443篇 |
1965年 | 331篇 |
1959年 | 198篇 |
1958年 | 293篇 |
1957年 | 193篇 |
1956年 | 172篇 |
1955年 | 167篇 |
1954年 | 159篇 |
1948年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Observations in nature and captivity reveal that members of the population of Rhinoclemmys areolata of western Tabasco, Mexico, exhibit underwater courtship and mating and appear to lay one egg per nest. 相似文献
182.
183.
Five additional species of wood rotting basidiomycetes on Arizona junipers are described and illustrated. All cause a white rot of dead, fallen trees. Leptosporomyces juniperinus is proposed as a new species. Vararia fibra is reported from the United States for the first time. 相似文献
184.
Autumn musters of bison ( Bison bison ) on Antelope Island State Park, Utah, conducted annually since 1987, provided data on temporal and age-specific reproductive patterns and a basis to evaluate the efficacy of management measures implemented to elevate reproductive performance in the herd. Pregnancy rates were variable and low ( x = 46.2%) in comparison to other free-ranging, noncommercial bison herds in North America. Cows in the 3- and > 6-yr range age classes exhibited lower-than-expected pregnancy rates ( P r = 0.64, P = 0.047) linear decline of 2.5% per annum. Variance in distribution of fetal ages observed in 6 yr indicates substantial temporal fluctuation. Long-term reproductive performance of cohorts born prior to implementation of management measures did not differ from that of cohorts born subsequent to these changes. 相似文献
185.
We translocated 196 Sage Grouse ( Centrocercus urophasianus into Sawtooth Valley, Idaho, during March-April 1986-87 to augment a small resident population. Forty-four grouse equipped with radio transmitters were monitored through spring and summer. Nest sites ( n = 6) had greater ( P = .032) horizontal cover than did independent random plots ( n = 7). During summer, grouse used sites ( n = 50) with taller live and dead shrub heights, greater shrub canopy cover, and more ground litter ( P n = 50) 50-300 m from use sites. Distance to edge and mountain sagebrush ( Artemisia tridentata vaseyana ) density best separated use sites from independent random plots in logistic regression analysis and correctly classified 64% of the use sites and 78% of the independent random plots. Sage Grouse used sties that had narrower frequency distributions for many variables than did independent plots ( P < .04), suggesting selection for uniform habitat. 相似文献
186.
The problem of prediction in time series using nonparametric functional techniques is considered. An extension of the local linear method to regression with functional explanatory variable is proposed. This forecasting method is compared with the functional Nadaraya–Watson method and with finite‐dimensional nonparametric predictors for several real‐time series. Prediction intervals based on the bootstrap and conditional distribution estimation for those nonparametric methods are also compared. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
187.
Jessica L. Slack Corey P. Causey Paul R. Thompson 《Cellular and molecular life sciences : CMLS》2011,68(4):709-720
The recent approvals of anticancer therapeutic agents targeting the histone deacetylases and DNA methyltransferases have highlighted
the important role that epigenetics plays in human diseases, and suggested that the factors controlling gene expression are
novel drug targets. Protein arginine deiminase 4 (PAD4) is one such target because its effects on gene expression parallel
those observed for the histone deacetylases. We demonstrated that F- and Cl-amidine, two potent PAD4 inhibitors, display micromolar
cytotoxic effects towards several cancerous cell lines (HL-60, MCF7 and HT-29); no effect was observed in noncancerous lines
(NIH 3T3 and HL-60 granulocytes). These compounds also induced the differentiation of HL-60 and HT29 cells. Finally, these
compounds synergistically potentiated the cell killing effects of doxorubicin. Taken together, these findings suggest PAD4
inhibition as a novel epigenetic approach for the treatment of cancer, and suggest that F- and Cl-amidine are candidate therapeutic
agents for this disease. 相似文献
188.
L. Vanderkelen J. M. Van Herreweghe K. G. A. Vanoirbeek G. Baggerman B. Myrnes P. J. Declerck I. W. Nilsen C. W. Michiels L. Callewaert 《Cellular and molecular life sciences : CMLS》2011,68(6):1053-1064
Lysozymes are antibacterial effectors of the innate immune system in animals that hydrolyze peptidoglycan. Bacteria have evolved
protective mechanisms that contribute to lysozyme tolerance such as the production of lysozyme inhibitors, but only inhibitors
of chicken (c-) and invertebrate (i-) type lysozyme have been identified. We here report the discovery of a novel Escherichia coli inhibitor specific for goose (g-) type lysozymes, which we designate PliG (periplasmic lysozyme inhibitor of g-type lysozyme).
Although it does not inhibit c- or i-type lysozymes, PliG shares a structural sequence motif with the previously described
PliI and MliC/PliC lysozyme inhibitor families, suggesting a common ancestry and mode of action. Deletion of pliG increased the sensitivity of E. coli to g-type lysozyme. The existence of inhibitors against all major types of animal lysozyme and their contribution to lysozyme
tolerance suggest that lysozyme inhibitors may play a role in bacterial interactions with animal hosts. 相似文献
189.
Eoin E. Kelly Conor P. Horgan Mary W. McCaffrey Paul Young 《Cellular and molecular life sciences : CMLS》2011,68(2):185-194
Long-term potentiation (LTP) defines persistent increases in neurotransmission strength at synapses that are triggered by
specific patterns of neuronal activity. LTP, the most widely accepted molecular model for learning, is best characterised
at glutamatergic synapses on dendritic spines. In this context, LTP involves increases in dendritic spine size and the insertion
of glutamate receptors into the post-synaptic spine membrane, which together boost post-synaptic responsiveness to neurotransmitters.
In dendrites, the material required for LTP is sourced from an organelle termed the endosomal-recycling compartment (ERC),
which is localised to the base of dendritic spines. When LTP is induced, material derived from the recycling compartment,
which contains α-amino-3-hydroxy-5-methyl-4-isoxazole propionate-type glutamate receptors (AMPARs), is mobilised into dendritic
spines feeding the increased need for receptors and membrane at the spine neck and head. In this review, we discuss the importance
of endosomal-recycling and the role of key proteins which control these processes in the context of LTP. 相似文献
190.