全文获取类型
收费全文 | 1090篇 |
免费 | 42篇 |
国内免费 | 71篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 13篇 |
2020年 | 20篇 |
2019年 | 30篇 |
2018年 | 29篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 30篇 |
2014年 | 91篇 |
2013年 | 101篇 |
2012年 | 62篇 |
2011年 | 59篇 |
2010年 | 49篇 |
2009年 | 69篇 |
2008年 | 68篇 |
2007年 | 70篇 |
2006年 | 54篇 |
2005年 | 38篇 |
2004年 | 39篇 |
2003年 | 30篇 |
2002年 | 32篇 |
2001年 | 22篇 |
2000年 | 9篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 16篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有1203条查询结果,搜索用时 156 毫秒
91.
Preissler T Luft T Kapczinski F Quevedo J Schwartsmann G Roesler R 《Neurochemical research》2007,32(8):1381-1386
Increasing evidence indicates that the gastrin-releasing peptide receptor (GRPR) is implicated in regulating synaptic plasticity
and memory formation in the hippocampus and other brain areas. However, the molecular mechanisms underlying the memory-impairing
effects of GRPR antagonism have remained unclear. Here we report that basic fibroblast growth factor (bFGF/FGF-2) rescues
the memory impairment induced by GRPR antagonism in the rat dorsal hippocampus. The GRPR antagonist [D-Tpi6, Leu13 psi(CH2NH)-Leu14] bombesin (6–14) (RC-3095) at 1.0 μg impaired, whereas bFGF at 0.25 μg enhanced, 24 h retention of inhibitory avoidance (IA)
when infused immediately after training into the CA1 hippocampal area in male rats. Coinfusion with an otherwise ineffective
dose of bFGF blocked the memory-impairing effect of RC-3095. These findings suggest that the memory-impairing effects of GRPR
antagonists might be partially mediated by an inhibition in the function and/or expression of neuronal bFGF or diminished
activation of intracellular protein kinase pathways associated with bFGF signaling. 相似文献
92.
93.
It has been proposed that proteins fold by a process called "Zipping and Assembly" (Z&A). Zipping refers to the growth of local substructures within the chain, and assembly refers to the coming together of already-formed pieces. Our interest here is in whether Z&A is a general method that can fold most of sequence space, to global minima, efficiently. Using the HP model, we can address this question by enumerating full conformation and sequence spaces. We find that Z&A reaches the global energy minimum native states, even though it searches only a very small fraction of conformational space, for most sequences in the full sequence space. We find that Z&A, a mechanism-based search, is more efficient in our tests than the replica exchange search method. Folding efficiency is increased for chains having: (a) small loop-closure steps, consistent with observations by Plaxco et al. 1998;277;985-994 that folding rates correlate with contact order, (b) neither too few nor too many nucleation sites per chain, and (c) assembly steps that do not occur too early in the folding process. We find that the efficiency increases with chain length, although our range of chain lengths is limited. We believe these insights may be useful for developing faster protein conformational search algorithms. 相似文献
94.
Mohammed I. Al-Daej Mohamed M. El-Malky Muhammad N. Sattar Adel A. Rezk Muhammad N. Naqqash Jameel M. Al-Khayri 《Phyton》2022,91(9):1905-1922
Rice stem borer (Chilo agamemnon Bles.) is a primary insect pest of rice and is a major limiting factor to rice
production. Breeding for insect-resistant crop varieties has been an economic way of integrated pest management
(IPM) as it offers a viable and ecologically acceptable approach. This study was aimed to evaluate rice genotypes
for their resistance against rice stem borer. Seven parental genotypes with twenty one F1 crosses were evaluated
for genotypic variation in field experiments. Analysis of variance revealed significant differences for the studied
traits in almost all crosses and parents. In addition, the mean squares of parents versus their crosses were signifi-
cant for stem borer resistance and other associated traits. Moreover, both general combining ability (GCA) and
specific combining ability (SCA) variances were highly significant for all characters studied in the F1 generation.
Based on GCA, 4 genotypes (Sakha101, Gz6903-3-4-2-1, Gz9577-4-1-1 and Hassawi) exhibited highly significant
negative values for stem borer resistance (–0.53, –1.06, –0.18 and –0.49, respectively) indicating they are the best
combiners for stem borer resistance. Based on SCA analysis, nine cross combinations showed highly significant
negative effects for stem borer resistance. Similarly, the cross Giza178 Hassawi was the best combination with
significantly highest value for early maturity. In addition, seven crosses showed highly significant negative
SCA for plant height trait. On the other hand, for panicle length, number of primary branches/panicle, panicle
weight and 1000-grain weight, seven, four, eight and six crosses showed highly significant positive SCA, respectively. The result further revealed that the non-additive dominance genetic variance was higher than the additive
variance for all evaluated traits indicating that non-additive genetic variances have a role in their inheritance. The
broad-sense heritability estimates were high for all the studied traits. The stem borer resistance was significantly
correlated with panicle weight and 1000-grain weight, which also showed a highly significant correlation with
grain yield/plant. Thus these traits can be effectively employed in a breeding program to confer resistance against
stem borer infestation in rice. It was further supported by biplot analysis, which clustered these potentially important traits into two quadrants showing their importance in any future breeding program to control stem borer
infestation. This study has contributed valuable information for evaluation of genetic diversity in the local rice
germplasm and its utilization in futuristic rice genetic improvement programs. 相似文献
95.
Alejandro Lpez-Castillo 《Chirality》2022,34(1):104-113
We show a chiral symmetry conservation principle based on chemical kinetics using stochastic results. Suppose the chiral symmetry conservation is evoked, and our universe can be considered globally asymmetric. In that case, there are at least two mirrored asymmetric universes if all the chiral properties are strongly correlated. However, if the chiral correlations are weak or nonexistent, there are possibly Many-(Chiral-Symmetry)-Worlds. Alternatively, if our universe is only locally asymmetric, there could be a single universe with segregated chiral regions. The possible mechanisms of the primordial chiral symmetry breaking can only be found if the chiral symmetry is not truly conserved by assuming the initial racemic conditions. In that case, our universe is asymmetric and could be alone. On the other hand, if the chiral symmetry is conserved, there is no chance of finding the primordial chiral symmetry breaking. Based on this conservation (or not), it is possible to infer two opposite hypotheses, where two general scenarios about the chiral universes are possible. 相似文献
96.
人才培养是未来国家竞争的核心。“强基计划”是我国对基础学科拔尖创新人才培养模式的重要探索,是满足国家重大战略人才需求的重要举措。“强基计划”招收的学生,往往成绩优异、兴趣浓厚,这为相关学科的人才培养模式提出了新要求和新目标。其中,“强基计划”背景下的基础教学改革势在必行。超学科教育理念(science,technology,engineering,arts,mathematics,STEAM)作为一种跨学科的综合性教育理念,与“强基计划”的建设理念不谋而合。鉴于此,天津大学生命科学学院根据“强基计划”背景下生物学科人才培养目标,结合STEAM教育理念,以“生物学综合设计”课程为例,对生物学实验教学改革进行了探索与实践。 相似文献
97.
98.
99.
According to the ultrastructural characteristic observation of the developing male germ cells, spermatogenesis of the crustacean
shrimp, Fenneropenaeus chinensis, is classified into spermatogonia, primary spermatocytes, secondary spermatocyte, four stages of spermatids, and mature sperm.
The basic protein transition during its spermatogenesis is studied by transmission electron microscopy of ammoniacal silver
reaction and immunoelectron microscopical distribution of acetylated histone H4. The results show that basic protein synthesized
in cytoplasm of spermatogonia is transferred into the nucleus with deposition on new duplicated DNA. In the spermatocyte stage,
some nuclear basic protein combined with RNP is transferred into the cytoplasm and is involved in forming the cytoplasmic
vesicle clumps. In the early spermatid, most of the basic protein synthesized in the new spermatid cytoplasm is transferred
into the nucleus, and the chromatin condensed gradually, and the rest is shifted into the pre-acrosomal vacuole. In the middle
spermatid, the nuclear basic protein linked with DNA is acetylated and transferred into the proacrosomal vacuole and assembled
into the acrosomal blastema. At the late spermatid, almost all of the basic protein in the nucleus has been removed into the
acrosome. During the stage from late spermatid to mature sperm, some de novo basic proteins synthesized in the cytoplasm belt
transfer into the nucleus without a membrane and almost all deposit in the periphery to form a supercoating. The remnant histone
H4 accompanied by chromatin fibers is acetylated in the center of the nucleus, leading to relaxed DNA and activated genes
making the nucleus non-condensed. 相似文献
100.
Sexual selection theory predicts that phenotypic traits used to choose a mate should reflect honestly the quality of the sender and thus, are often costly. Physiological costs arise if a signal depends on limited nutritional resources. Hence, the nutritional condition of an organism should determine both its quality as a potential mate and its ability to advertise this quality to the choosing sex. In insects, the quality of the offspring's nutrition is often determined by the ovipositing female. A causal connection, however, between the oviposition decisions of the mother and the mating chances of her offspring has never been shown. Here, we demonstrate that females of the parasitic wasp Nasonia vitripennis prefer those hosts for oviposition that have been experimentally enriched in linoleic acid (LA). We show by (13)C-labelling that LA from the host diet is a precursor of the male sex pheromone. Consequently, males from LA-rich hosts produce and release higher amounts of the pheromone and attract more virgin females than males from LA-poor hosts. Finally, males from LA-rich hosts possess three times as many spermatozoa as those from LA-poor hosts. Hence, females making the right oviposition decisions may increase both the fertility and the sexual attractiveness of their sons. 相似文献