全文获取类型
收费全文 | 62833篇 |
免费 | 5221篇 |
国内免费 | 3448篇 |
出版年
2024年 | 134篇 |
2023年 | 655篇 |
2022年 | 1560篇 |
2021年 | 2547篇 |
2020年 | 1733篇 |
2019年 | 2221篇 |
2018年 | 2382篇 |
2017年 | 2015篇 |
2016年 | 2683篇 |
2015年 | 3333篇 |
2014年 | 4045篇 |
2013年 | 4506篇 |
2012年 | 5191篇 |
2011年 | 4865篇 |
2010年 | 3457篇 |
2009年 | 3056篇 |
2008年 | 3523篇 |
2007年 | 3241篇 |
2006年 | 2841篇 |
2005年 | 2462篇 |
2004年 | 2356篇 |
2003年 | 2164篇 |
2002年 | 1824篇 |
2001年 | 1119篇 |
2000年 | 916篇 |
1999年 | 745篇 |
1998年 | 524篇 |
1997年 | 422篇 |
1996年 | 402篇 |
1995年 | 397篇 |
1994年 | 364篇 |
1993年 | 295篇 |
1992年 | 358篇 |
1991年 | 304篇 |
1990年 | 267篇 |
1989年 | 254篇 |
1988年 | 177篇 |
1987年 | 223篇 |
1986年 | 196篇 |
1985年 | 161篇 |
1984年 | 155篇 |
1983年 | 137篇 |
1982年 | 135篇 |
1981年 | 120篇 |
1980年 | 90篇 |
1979年 | 92篇 |
1978年 | 94篇 |
1977年 | 76篇 |
1976年 | 77篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
121.
122.
123.
124.
Mathieu Lefèvre Daniel J. Felmlee Marie Parnot Thomas F. Baumert Catherine Schuster 《PloS one》2014,9(4)
Hepatitis C virus (HCV) is a major cause of liver disease worldwide and HCV infection represents a major health problem. HCV associates with host lipoproteins forming host/viral hybrid complexes termed lipoviral particles. Apolipoprotein E (apoE) is a lipoprotein component that interacts with heparan sulfate proteoglycans (HSPG) to mediate hepatic lipoprotein uptake, and may likewise mediate HCV entry. We sought to define the functional regions of apoE with an aim to identify critical apoE binding partners involved in HCV infection. Using adenoviral vectors and siRNA to modulate apoE expression we show a direct correlation of apoE expression and HCV infectivity, whereas no correlation exists with viral protein expression. Mutating the HSPG binding domain (HSPG-BD) of apoE revealed key residues that are critical for mediating HCV infection. Furthermore, a novel synthetic peptide that mimics apoE’s HSPG-BD directly and competitively inhibits HCV infection. Genetic knockdown of the HSPG proteins syndecan (SDC) 1 and 4 revealed that SDC4 principally mediates HCV entry. Our data demonstrate that HCV uses apoE-SDC4 interactions to enter hepatoma cells and establish infection. Targeting apoE-SDC interactions could be an alternative strategy for blocking HCV entry, a critical step in maintaining chronic HCV infection. 相似文献
125.
Yu. S. Ravkin S. M. Tsybulin S. G. Livanov K. V. Toropov V. N. Kuranova V. P. Starikov S. V. Chesnokova 《Contemporary Problems of Ecology》2008,1(5):568-573
For the entire territory of West Siberia, including its plain and mountainous parts, two maps were constructed for populations of amphibians together with reptiles, and of birds. Communities of these classes of vertebrates differ from one another in their spatial differentiation. The differences are demonstrated for the plain and mountainous territories considered jointly and separately. 相似文献
126.
Alan C. L. Yu 《PloS one》2010,5(8)
Variation is a ubiquitous feature of speech. Listeners must take into account context-induced variation to recover the interlocutor''s intended message. When listeners fail to normalize for context-induced variation properly, deviant percepts become seeds for new perceptual and production norms. In question is how deviant percepts accumulate in a systematic fashion to give rise to sound change (i.e., new pronunciation norms) within a given speech community. The present study investigated subjects'' classification of /s/ and // before /a/ or /u/ spoken by a male or a female voice. Building on modern cognitive theories of autism-spectrum condition, which see variation in autism-spectrum condition in terms of individual differences in cognitive processing style, we established a significant correlation between individuals'' normalization for phonetic context (i.e., whether the following vowel is /a/ or /u/) and talker voice variation (i.e., whether the talker is male or female) in speech and their “autistic” traits, as measured by the Autism Spectrum Quotient (AQ). In particular, our mixed-effect logistic regression models show that women with low AQ (i.e., the least “autistic”) do not normalize for phonetic coarticulation as much as men and high AQ women. This study provides first direct evidence that variability in human''s ability to compensate for context-induced variations in speech perceptually is governed by the individual''s sex and cognitive processing style. These findings lend support to the hypothesis that the systematic infusion of new linguistic variants (i.e., the deviant percepts) originate from a sub-segment of the speech community that consistently under-compensates for contextual variation in speech. 相似文献
127.
The possibility of the use of small amounts of chitosan for defatting and clarification of protein solutions prepared by enzymatic hydrolysis was tested. The following treatment conditions were shown to be optimal: a chitosan concentration range, from 1.0 to 1.5 gram per kilogram raw weight; pH of the precipitation medium from 8.0 to 8.5; and duration of the incubation of the protein hydrolysate solution with chitosan, less than 1 h. The hydrolysate defatting grade was found to depend on the degree of chitosan deacetylation. A possible mechanism of the chitosan-induced effects was suggested. The use of chitosan allows the mass fraction of enzyme protein hydrolysates to be reduced fourfold to fivefold. 相似文献
128.
129.
Mark T Uhlik Amy N Abell Bruce D Cuevas Kazuhiro Nakamura Gary L Johnson 《Biochimie et biologie cellulaire》2004,82(6):658-663
Mitogen-activated protein kinase (MAPK) pathways are activated by a plethora of stimuli. The literature is filled with papers describing the activation of different MAPKs by almost any stimulus or insult imaginable to cells. In this review, we use signal transduction wiring diagrams to illustrate putative upstream regulators for the MAPK kinase kinases, MEKK1, 2, and 3. Targeted gene disruption of MEKK1, 2, or 3 defined phenotypes for each MEKK associated with loss of specific MAPK regulation. Genetic analysis of MEKK function clearly defines specific components of the wiring diagram that require MEKK1, 2, or 3 for physiological responses. We propose that signal transduction network wiring diagrams are valuable tools for hypothesis building and filtering physiologically relevant phenotypic responses from less connected protein relations in the regulation of MAPK pathways. 相似文献
130.
Aiyi Liu James F. Troendle Kai F. Yu Vivian W. Yuan 《Biometrical journal. Biometrische Zeitschrift》2004,46(6):760-768
We consider estimation after a group sequential test. An estimator that is unbiased or has small bias may have substantial conditional bias (Troendle and Yu, 1999, Coburger and Wassmer, 2001). In this paper we derive the conditional maximum likelihood estimators of both the primary parameter and a secondary parameter, and investigate their properties within a conditional inference framework. The method applies to both the usual and adaptive group sequential test designs. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献