全文获取类型
收费全文 | 157148篇 |
免费 | 6041篇 |
国内免费 | 860篇 |
出版年
2022年 | 380篇 |
2021年 | 1162篇 |
2020年 | 651篇 |
2019年 | 897篇 |
2018年 | 12752篇 |
2017年 | 11362篇 |
2016年 | 9015篇 |
2015年 | 3458篇 |
2014年 | 3481篇 |
2013年 | 4116篇 |
2012年 | 8950篇 |
2011年 | 17059篇 |
2010年 | 14583篇 |
2009年 | 10570篇 |
2008年 | 13294篇 |
2007年 | 14565篇 |
2006年 | 3497篇 |
2005年 | 3475篇 |
2004年 | 3811篇 |
2003年 | 3598篇 |
2002年 | 3030篇 |
2001年 | 2075篇 |
2000年 | 1878篇 |
1999年 | 1418篇 |
1998年 | 674篇 |
1997年 | 589篇 |
1996年 | 513篇 |
1995年 | 500篇 |
1994年 | 432篇 |
1993年 | 421篇 |
1992年 | 811篇 |
1991年 | 705篇 |
1990年 | 644篇 |
1989年 | 632篇 |
1988年 | 562篇 |
1987年 | 544篇 |
1986年 | 447篇 |
1985年 | 435篇 |
1984年 | 411篇 |
1983年 | 348篇 |
1982年 | 305篇 |
1980年 | 299篇 |
1979年 | 333篇 |
1978年 | 316篇 |
1977年 | 291篇 |
1976年 | 267篇 |
1974年 | 298篇 |
1973年 | 272篇 |
1972年 | 454篇 |
1971年 | 467篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
11.
The Asian Tree Toad genus Pedostibes, as currently understood, exhibits a conspicuously disjunct distribution, posing several immediate questions relating to the biogeography and taxonomy of this poorly known group. The type species, P. tuberculosus and P. kempi, are known only from India, whereas P. hosii, P. rugosus, and P. everetti are restricted to Southeast Asia. Several studies have shown that these allopatric groups are polyphyletic, with the Indian Pedostibes embedded within a primarily South Asian clade of toads, containing the genera Adenomus, Xanthophryne, and Duttaphrynus. Southeast Asian Pedostibes on the other hand, are nested within a Southeast Asian clade, which is the sister lineage to the Southeast Asian river toad genus Phrynoidis. We demonstrate that Indian and Southeast Asian Pedostibes are not only allopatric and polyphyletic, but also exhibit significant differences in morphology and reproductive mode, indicating that the Southeast Asian species’ are not congeneric with the true Pedostibes of India. As a taxonomic solution, we describe a new genus, Rentapia
gen. nov. to accommodate the Southeast Asian species. 相似文献
12.
13.
14.
HIF-1 expression in healing wounds: HIF-1alpha induction in primary inflammatory cells by TNF-alpha 总被引:12,自引:0,他引:12
15.
Background
Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation. 相似文献16.
State of aggregation of the (Ca2+ + Mg2+)-ATPase studied using saturation-transfer electron spin resonance 总被引:1,自引:0,他引:1
The state of aggregation of the (Ca2+ + Mg2+)-ATPase in the membrane of sarcoplasmic reticulum and in reconstituted membrane systems has been studied using saturation-transfer electron spin resonance (ST-ESR). Saturation-transfer ESR spectra show that in the sarcoplasmic reticulum, the ATPase is relatively free to rotate, with an effective rotational correlation time of approx. 33 microseconds at 4 degrees C, consistent with a monomeric or dimeric structure. The rate of rotation is observed to decrease with decreasing molar ratio of lipid to protein. In reconstituted systems, rotational motion of the ATPase on the millisecond time scale ceases when the lipids are in the gel phase. Addition of decavanadate, which causes the formation of crystalline arrays in negatively stained electron micrographs, results in only a small reduction in rotation rate for the ATPase in the membrane. The experiments are interpreted in terms of a short-lived (on the millisecond time scale) protein-protein interaction, with the formation of crystalline clusters of ATPase molecules which form and melt rapidly. 相似文献
17.
18.
19.
Henry C. Stevens Elaine M. Metz Percy Saboya Del Castillo Juan Díaz Alvn Mark T. Bowler 《Journal of Field Ornithology》2019,90(1):70-79
White‐sand forests are patchily distributed ecosystems covering just 5% of Amazonia that host many specialist species of birds not found elsewhere, and these forests are threatened due to their small size and human exploitation of sand for construction projects. As a result, many species of birds that are white‐sand specialists are at risk of extinction, and immediate conservation action is paramount for their survival. Our objective was to evaluate current survey methods and determine the relative effect of the size of patches of these forests on the presence or absence of white‐sand specialists. Using point counts and autonomous recorders, we surveyed avian assemblages occupying patches of white‐sand forest in the Peruvian Amazon in April 2018. Overall, we detected 126 species, including 21 white‐sand forest specialists. We detected significantly more species of birds per survey point with autonomous recorders than point counts. We also found a negative relationship between avian species richness and distance from the edge of patches of white‐sand forest, but a significant, positive relationship when only counting white‐sand specialists. Although we detected more species with autonomous recorders, point counts were more effective for detecting canopy‐dwelling passerines. Therefore, we recommend that investigators conducting surveys for rare and patchily distributed species in the tropics use a mixed‐method approach that incorporates both autonomous recorders and visual observation. Finally, our results suggest that conserving large, continuous patches of white‐sand forest may increase the likelihood of survival of species of birds that are white‐sand specialists. 相似文献
20.