全文获取类型
收费全文 | 4106篇 |
免费 | 403篇 |
国内免费 | 2篇 |
出版年
2023年 | 18篇 |
2022年 | 61篇 |
2021年 | 86篇 |
2020年 | 51篇 |
2019年 | 66篇 |
2018年 | 82篇 |
2017年 | 52篇 |
2016年 | 106篇 |
2015年 | 184篇 |
2014年 | 201篇 |
2013年 | 218篇 |
2012年 | 312篇 |
2011年 | 285篇 |
2010年 | 171篇 |
2009年 | 154篇 |
2008年 | 244篇 |
2007年 | 253篇 |
2006年 | 215篇 |
2005年 | 229篇 |
2004年 | 220篇 |
2003年 | 167篇 |
2002年 | 168篇 |
2001年 | 50篇 |
2000年 | 35篇 |
1999年 | 50篇 |
1998年 | 53篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 19篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 35篇 |
1991年 | 26篇 |
1990年 | 37篇 |
1989年 | 32篇 |
1988年 | 27篇 |
1987年 | 33篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 30篇 |
1982年 | 26篇 |
1981年 | 37篇 |
1980年 | 19篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1975年 | 18篇 |
1974年 | 26篇 |
1973年 | 18篇 |
排序方式: 共有4511条查询结果,搜索用时 93 毫秒
1.
Modern nutritional studies have found that diverse diets are linked to lower infant mortality rates and longer life expectancies in humans. This is primarily because humans require more than fifty essential nutrients for growth and cell maintenance and repair; most of these essential nutrients must come from outside food sources rather than being manufactured by the body itself; and a diversity of food types is required to consume the full suite of essential nutrients necessary for optimal human health. These principles and their related affects on human adaptations and demography are the hallmarks of a theoretical paradigm defined as nutritional ecology. This essay applies concepts derived from nutritional ecology to the study of human evolution. Principles of nutritional ecology are applied to the study of the Middle‐to‐Upper Paleolithic transition in order to broadly illustrate the interpretive ramifications of this approach. At any stage in human evolution, those hominid populations that chose to diversify their subsistence base may have had a selective advantage over competitors who restricted their diet principally to one food type, such as terrestrial mammals. 相似文献
2.
3.
Plant and Soil - Agricultural practices often have persistent effects on soil physicochemical properties and soil biota, which can feedback to influence plant performance. We investigated... 相似文献
4.
5.
Bryan M. Turner 《Chromosoma》1982,87(3):345-357
A mouse monoclonal IgM antibody against the core histone H2B has been shown, by indirect immunofluorescence, to stain metaphase chromosomes from a variety of cultured cell types. Experiments carried out with human HeLa cells showed that the intensity of staining varied along the length of chromosome arms giving in some cases a rudimentary banded staining pattern. Considerable variation in staining intensity was noted between individual chromosomes and between different metaphase spreads. It was noted that chromosomes having a more swollen appearance stained more intensely than those with a more compact structure, which were often unstained. Preincubation of unfixed metaphase chromosomes in buffered salt solutions virtually eliminated the cell to cell and chromosome to chromosome variation in staining, even when no visible effect on chromosome morphology was caused by such treatment. It is concluded that the determinant recognised by antibody HBC-7 is ubiquitous but is inaccessible in some chromosomes or chromosome regions. Digestion of purified chromatin (primarily interphase) with DNAase 1 or micrococcal nuclease resulted in a several-fold increase in the binding of antibody HBC-7 measured by solid-phase radioimmunoassay. This increase was abolished by subsequent treatment with trypsin, which suggests that the antigenic determinant recognised by antibody HBC-7 lies in the trypsin-sensitive N-terminal region of nucleosomal H2B. As the cationic N-terminal regions of the core histones are involved in DNA binding, it is likely that the accessibility of the determinant recognised by antibody HBC-7 is influenced by the relationship between the core histones and their associated DNA. 相似文献
6.
Susanne Berglund Bryan J. Egner Henrik Gradén Joakim Gradén David G.A. Morgan Tord Inghardt Fabrizio Giordanetto 《Bioorganic & medicinal chemistry letters》2009,19(15):4268-4273
Herein, we disclose the discovery and optimization of 2-piperidin-4-yl-acetamide derivatives as MCH-R1 antagonists. Structural investigation of piperidin-4-yl-amide and piperidin-4-yl-ureas identified 2-piperidin-4-yl-acetamide-based MCH-R1 antagonists with outstanding in vivo efficacy but flawed with high affinity towards the hERG potassium channel. While existing hERG SAR information was employed to discover highly potent MCH-R1 antagonists with minimized hERG inhibition, additional hurdles prevented their subsequent clinical exploration. 相似文献
7.
8.
Bryan Byrne 《American anthropologist》2000,102(2):369-370
The Material Life of Human Beings: Artifacts, Behavior, and Communication. Michael Brian Schiffer with Andrea R. Miller. New York: Routledge, 1999. 158 pp. 相似文献
9.
Novel endogenous human retroviral sequences were cloned by low-stringency hybridization, using the pol gene of endogenous human retrovirus 51-1. One clone, lambda NP-2, contained gag, pol, env, and long terminal repeat sequences related to the corresponding portions of clone 51-1 and the closely related full-length endogenous human retrovirus 4-1. The sequence of the env gene of NP-2 was 73% homologous to that of 4-1. Genomic Southern blots of male and female DNAs showed that NP-2 is located on the Y chromosome and that the Y chromosome also contains one other sequence closely related to the env and 3' flanking regions of NP-2. Conservation of flanking DNA suggests that the second Y chromosome copy of the NP-2 env sequence arose by gene duplication rather than provirus insertion. 相似文献
10.
Bryan D. Noe Sharon L. Milgram A. Balasubramaniam P. C. Andrews Jaroslaw Calka John K. McDonald 《Cell and tissue research》1989,257(2):303-311
Summary Results from a previous report demonstrate that more than one molecular form of neuropeptide Y-like peptide may be present in the islet organ of the anglerfish (Lophius americanus). Most of the neuropeptide Y-like immunoreactive material was anglerfish peptide YG, which is expressed in a subset of islet cells, whereas an additional neuropeptide Y-like peptide(s) was localized in islet nerves. To learn more about the neuropeptide Y-like peptides in islet nerves, we have employed immunohistochemical and biochemical methods to compare peptides found in anglerfish islets and brain. Using antisera that selectively react with either mammalian forms of neuropeptide Y or with anglerfish peptide YG, subsets of neurons were found in the brain that labelled with only one or the other of the antisera. In separate sections, other neurons that were labelled with either antiserum exhibited similar morphologies. Peptides from brains and islets were subjected to gel filtration and reverse-phase high performance liquid chromatography. Radioimmunoassays employing either the neuropeptide Y or peptide YG antisera were used to examine chromatographic eluates. Immunoreactive peptides having retention times of human neuropeptide Y and porcine neuropeptide Y were identified in extracts of both brain and islets. This indicates that peptides structurally similar to both of these peptides from the neuropeptide Y-pancreatic polypeptide family are expressed in neurons of anglerfish brain and nerve fibers of anglerfish islets. The predominant form of neuropeptide Y-like peptide in islets was anglerfish peptide YG. Neuropeptide Y-immunoreactive peptides from islet extracts that had chromatographic retention times identical to human neuropeptide Y and porcine neuropeptide Y were present in much smaller quantities. These results are consistent with the hypothesis that peptides having significant sequence homology with human neuropeptide Y and porcine neuropeptide Y are present in the nerve fibers that permeate the islet. 相似文献