全文获取类型
收费全文 | 117104篇 |
免费 | 7057篇 |
国内免费 | 13篇 |
出版年
2023年 | 716篇 |
2022年 | 652篇 |
2021年 | 1441篇 |
2020年 | 1356篇 |
2019年 | 1339篇 |
2018年 | 3276篇 |
2017年 | 2940篇 |
2016年 | 3927篇 |
2015年 | 5155篇 |
2014年 | 5252篇 |
2013年 | 7033篇 |
2012年 | 8235篇 |
2011年 | 7321篇 |
2010年 | 4731篇 |
2009年 | 3560篇 |
2008年 | 5895篇 |
2007年 | 5580篇 |
2006年 | 5396篇 |
2005年 | 4568篇 |
2004年 | 4541篇 |
2003年 | 4112篇 |
2002年 | 3738篇 |
2001年 | 2891篇 |
2000年 | 2795篇 |
1999年 | 2138篇 |
1998年 | 944篇 |
1997年 | 676篇 |
1996年 | 720篇 |
1995年 | 646篇 |
1994年 | 586篇 |
1992年 | 1221篇 |
1991年 | 1100篇 |
1990年 | 1048篇 |
1989年 | 1131篇 |
1988年 | 960篇 |
1987年 | 936篇 |
1986年 | 885篇 |
1985年 | 925篇 |
1984年 | 811篇 |
1983年 | 677篇 |
1979年 | 768篇 |
1978年 | 591篇 |
1975年 | 672篇 |
1974年 | 734篇 |
1973年 | 718篇 |
1972年 | 646篇 |
1971年 | 569篇 |
1970年 | 619篇 |
1969年 | 677篇 |
1968年 | 648篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
262.
María Prados-Privado Juan Carlos Prados-Frutos José Luis Calvo-Guirado José Antonio Bea 《Computer methods in biomechanics and biomedical engineering》2016,19(15):1583-1591
To measure fatigue in dental implants and in its components, it is necessary to use a probabilistic analysis since the randomness in the output depends on a number of parameters (such as fatigue properties of titanium and applied loads, unknown beforehand as they depend on mastication habits). The purpose is to apply a probabilistic approximation in order to predict fatigue life, taking into account the randomness of variables. More accuracy on the results has been obtained by taking into account different load blocks with different amplitudes, as happens with bite forces during the day and allowing us to know how effects have different type of bruxism on the piece analysed. 相似文献
263.
To date, the effects of long-term growth hormone (GH)-releasing hormone [GHRH(1-29)-NH2] treatment on the plasma concentrations of somatostatin-like immunoreactivity (SLI) remain undefined. In the present study, the effect of GHRH(1-29)-NH2 therapy on plasma SLI levels has been studied in 11 non-GH-deficient children. The pattern of administration was 5 micrograms/kg body weight, given subcutaneously once every day. There was no significant change in plasma SLI levels after bolus injection of GHRH(1-29)-NH2 before and during GHRH(1-29)-NH2 therapy. However, plasma SLI rose in basal plasma and nocturnal sleep after 3 months of GHRH(1-29)-NH2 therapy and remained the same during 6 months of treatment with GHRH(1-29)-NH2. The reason for this finding is uncertain, but an increase in SLI release from the enteroinsular axis is a possible explanation. The association of our findings with the role of the circulating SLI on nutrient homeostasis and the effects of GNRH on growth velocity is discussed. 相似文献
264.
265.
266.
Victor M. Luque-Almagro Verity J. Lyall Stuart J. Ferguson M. Dolores Roldán David J. Richardson Andrew J. Gates 《The Journal of biological chemistry》2013,288(41):29692-29702
Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression. 相似文献
267.
Fragments of Candida boidinii chromosomal DNA were inserted into the integrative vector YIp-kanr and examined for the presence of sequences promoting autonomous replication of plasmids in Saccharomyces cerevisiae. Restriction maps of two plasmids, designated S6/4 and S6/5, originating from the same S. cerevisiae transformant, were constructed. Southern hybridization data confirmed that the plasmids carry sequences from the C. boidinii chromosome. Both plasmids transform S. cerevisiae strains at 4-5-fold higher frequency than cloning vectors based on the replication origin of the 2 microns plasmid. Mitotic stability of the constructed plasmids is similar to that of the 2 mu-based vector pNF2 in S. cerevisiae. 相似文献
268.
269.
270.