全文获取类型
收费全文 | 209545篇 |
免费 | 13948篇 |
国内免费 | 1239篇 |
出版年
2021年 | 1100篇 |
2019年 | 1122篇 |
2018年 | 13009篇 |
2017年 | 11710篇 |
2016年 | 8924篇 |
2015年 | 2517篇 |
2014年 | 2681篇 |
2013年 | 3350篇 |
2012年 | 7529篇 |
2011年 | 16011篇 |
2010年 | 14027篇 |
2009年 | 10208篇 |
2008年 | 12309篇 |
2007年 | 13871篇 |
2006年 | 2826篇 |
2005年 | 2846篇 |
2004年 | 3191篇 |
2003年 | 3235篇 |
2002年 | 2957篇 |
2001年 | 9927篇 |
2000年 | 9700篇 |
1999年 | 7248篇 |
1998年 | 1646篇 |
1997年 | 1834篇 |
1996年 | 1611篇 |
1995年 | 1418篇 |
1994年 | 1327篇 |
1993年 | 1300篇 |
1992年 | 4826篇 |
1991年 | 4584篇 |
1990年 | 4014篇 |
1989年 | 4050篇 |
1988年 | 3643篇 |
1987年 | 3128篇 |
1986年 | 2798篇 |
1985年 | 2701篇 |
1984年 | 1996篇 |
1983年 | 1767篇 |
1982年 | 1244篇 |
1981年 | 992篇 |
1980年 | 923篇 |
1979年 | 1774篇 |
1978年 | 1374篇 |
1977年 | 1206篇 |
1976年 | 1036篇 |
1975年 | 1169篇 |
1974年 | 1182篇 |
1973年 | 1167篇 |
1972年 | 1287篇 |
1971年 | 1235篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
CHLOROPLASTS are more permeable to amino-acids1,2 than are cell membranes3 and also discriminate between their optical isomers2. This has led to the suggestion that the passage of amino-acids through the limiting membranes of chloroplasts is facilitated by carriers2. Using the additional criteria of saturation and competition, we support this suggestion and show that at least two carriers are probably involved. 相似文献
104.
The probability that protected areas will deliver their potential for maintaining or enhancing biodiversity is likely to be
maximised if they are appropriately and effectively managed. As a result, governments and conservation agencies are devoting
much attention to the management of protected areas. In the U.K., the demand for performance accountability has resulted in
Public Service Agreements (PSA) that set out targets for government departments to deliver results in return for investments
being made. One such target for England is to ensure that all nationally important wildlife sites are in favourable condition
by 2010. Here, we tested the hypothesis, of potential strategic importance, that the ecological condition of these sites is
predictable from relationships with a range of physical, environmental and demographic variables. We used binary logistic
regression to investigate these relationships, using the results of English Nature’s 1997–2003 condition assessment exercise.
Generally, sites in unfavourable condition tend to be larger in area, located at higher elevations, but with higher human
population density and are more spatially isolated from units of the same habitat. However, despite the range of different
parameters included in our models, the extent to which the condition of any given site could be predicted was low. Our results
have implications for the delivery of PSA targets, funding allocation, and the location of new protected areas. 相似文献
105.
Described here is a three-day protocol that directly yields DNA sequence after isolating and PCR amplifying genomic DNA from a small sample of frozen nasopharyngeal carcinoma tissue embedded in optimal cutting temperature (OCT) compound. The method is consistently successful, reproducible and will facilitate the rapid analysis of DNA sequence from very small samples. 相似文献
106.
107.
Comparisons among 16S rRNA sequences from various eubacteria reveal a natural relationship between the bacteroides (represented by the Bacteroides fragilis sequence) and a phylogenetic unit that comprises the flavobacteria, cytophagae, flexibacteria, and others (represented by the Flavobacterium heparinum sequence). Although the relationship is not a close one, it is, nevertheless, specific. rRNAs from these two organisms are not only closer to one another in overall sequence than they are to outgroup species (such as Bacillus subtilis, Escherichia coli, Desulfovibrio desulfuricans, and Agrobacterium tumefaciens), but they show common idiosyncrasies (i.e., derived characteristics) in both rRNA sequences and higher-order structures. 相似文献
108.
Daren Lee Seth Ruffins Queenie Ng Nikhil Sane Steve Anderson Arthur Toga 《BMC bioinformatics》2010,11(1):608
Background
Digital atlases provide a common semantic and spatial coordinate system that can be leveraged to compare, contrast, and correlate data from disparate sources. As the quality and amount of biological data continues to advance and grow, searching, referencing, and comparing this data with a researcher's own data is essential. However, the integration process is cumbersome and time-consuming due to misaligned data, implicitly defined associations, and incompatible data sources. This work addressing these challenges by providing a unified and adaptable environment to accelerate the workflow to gather, align, and analyze the data. 相似文献109.
James B Munro Roger B Altman Chang‐Shung Tung Kevin Y Sanbonmatsu Scott C Blanchard 《The EMBO journal》2010,29(4):770-781
A key intermediate in translocation is an ‘unlocked state’ of the pre‐translocation ribosome in which the P‐site tRNA adopts the P/E hybrid state, the L1 stalk domain closes and ribosomal subunits adopt a ratcheted configuration. Here, through two‐ and three‐colour smFRET imaging from multiple structural perspectives, EF‐G is shown to accelerate structural and kinetic pathways in the ribosome, leading to this transition. The EF‐G‐bound ribosome remains highly dynamic in nature, wherein, the unlocked state is transiently and reversibly formed. The P/E hybrid state is energetically favoured, but exchange with the classical P/P configuration persists; the L1 stalk adopts a fast dynamic mode characterized by rapid cycles of closure and opening. These data support a model in which P/E hybrid state formation, L1 stalk closure and subunit ratcheting are loosely coupled, independent processes that must converge to achieve the unlocked state. The highly dynamic nature of these motions, and their sensitivity to conformational and compositional changes in the ribosome, suggests that regulating the formation of this intermediate may present an effective avenue for translational control. 相似文献
110.
Y. Crouau 《Behavioural processes》1985,11(1):21-30
The cavernicolous crustacean Antromysis juberthiei showed unexpected behavior when presented with food extract : it avoids the area of odor inflow. This avoidance reaction is reduced by removal of various combinations of antennae and disappears almost with bilateral removal of the first antennae (the aesthetasc-bearing antennules). 相似文献