全文获取类型
收费全文 | 3253篇 |
免费 | 355篇 |
国内免费 | 2篇 |
专业分类
3610篇 |
出版年
2022年 | 23篇 |
2021年 | 40篇 |
2020年 | 16篇 |
2019年 | 34篇 |
2018年 | 30篇 |
2017年 | 43篇 |
2016年 | 65篇 |
2015年 | 131篇 |
2014年 | 124篇 |
2013年 | 210篇 |
2012年 | 211篇 |
2011年 | 207篇 |
2010年 | 137篇 |
2009年 | 123篇 |
2008年 | 173篇 |
2007年 | 164篇 |
2006年 | 197篇 |
2005年 | 185篇 |
2004年 | 189篇 |
2003年 | 157篇 |
2002年 | 162篇 |
2001年 | 68篇 |
2000年 | 50篇 |
1999年 | 80篇 |
1998年 | 66篇 |
1997年 | 29篇 |
1996年 | 33篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 36篇 |
1992年 | 44篇 |
1991年 | 31篇 |
1990年 | 38篇 |
1989年 | 37篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1984年 | 39篇 |
1983年 | 24篇 |
1982年 | 15篇 |
1981年 | 22篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1974年 | 20篇 |
1973年 | 15篇 |
1971年 | 14篇 |
排序方式: 共有3610条查询结果,搜索用时 15 毫秒
981.
Vered Eshed Avi Gopher Ron Pinhasi Israel Hershkovitz 《American journal of physical anthropology》2010,143(1):121-133
This study addresses changes in health which were consequential to the Neolithic transition in the southern Levant, judged on the basis of the study of specific and nonspecific stress indicators, trauma, and degenerative joint disease in 200 Natufian (hunter‐gatherer) skeletons (10,500–8300 BC) and 205 Neolithic (agricultural) skeletons (8300–5500 BC) from the southern Levant. The comparison of the health profiles of pre‐Neolithic (Natufian) and Neolithic populations reveals a higher prevalence of lesions indicative of infectious diseases among the Neolithic population, and an overall reduction in the prevalence of skull trauma among males. No change over time was observed in the prevalence of degenerative joint disease. These results indicate that in the southern Levant the Neolithic transition did not simply lead to an overall deterioration in health but rather resulted in a complex health profile which was shaped by 1) an increase exposure to disease agents, 2) changes in diet, 3) population aggregation in larger and denser settlements, 4) changes in activity patterns and the division of labor, and possibly 5) a higher resistant immunological system and response capacity to environmental aggressions (mainly infections). Am J Phys Anthropol 143:121–133, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
982.
983.
Whole brain segmentation: automated labeling of neuroanatomical structures in the human brain 总被引:26,自引:0,他引:26
Fischl B Salat DH Busa E Albert M Dieterich M Haselgrove C van der Kouwe A Killiany R Kennedy D Klaveness S Montillo A Makris N Rosen B Dale AM 《Neuron》2002,33(3):341-355
We present a technique for automatically assigning a neuroanatomical label to each voxel in an MRI volume based on probabilistic information automatically estimated from a manually labeled training set. In contrast to existing segmentation procedures that only label a small number of tissue classes, the current method assigns one of 37 labels to each voxel, including left and right caudate, putamen, pallidum, thalamus, lateral ventricles, hippocampus, and amygdala. The classification technique employs a registration procedure that is robust to anatomical variability, including the ventricular enlargement typically associated with neurological diseases and aging. The technique is shown to be comparable in accuracy to manual labeling, and of sufficient sensitivity to robustly detect changes in the volume of noncortical structures that presage the onset of probable Alzheimer's disease. 相似文献
984.
Sorting by reciprocal translocations via reversals theory. 总被引:1,自引:0,他引:1
The understanding of genome rearrangements is an important endeavor in comparative genomics. A major computational problem in this field is finding a shortest sequence of genome rearrangements that transforms, or sorts, one genome into another. In this paper we focus on sorting a multi-chromosomal genome by translocations. We reveal new relationships between this problem and the well studied problem of sorting by reversals. Based on these relationships, we develop two new algorithms for sorting by reciprocal translocations, which mimic known algorithms for sorting by reversals: a score-based method building on Bergeron's algorithm, and a recursive procedure similar to the Berman-Hannenhalli method. Though their proofs are more involved, our procedures for reciprocal translocations match the complexities of the original ones for reversals. 相似文献
985.
986.
The interaction of water with the water oxidizing Mn complex of photosystem II has been investigated using electron spin-echo envelope modulation spectroscopy in the presence of H(2)(17)O. The spectra show interaction of the (17)O with the preparation in the S(2) state induced by 200 K illumination. The modulation is observed only in the center of the multiline spectrum. The inferred hyperfine coupling terms are compatible with water (not hydroxyl) oxygen bound to a particular quasi-axial Mn(III) center in a coupled Mn cluster. 相似文献
987.
Pace CN Fu H Fryar KL Landua J Trevino SR Shirley BA Hendricks MM Iimura S Gajiwala K Scholtz JM Grimsley GR 《Journal of molecular biology》2011,408(3):514-547
Our goal was to gain a better understanding of the contribution of hydrophobic interactions to protein stability. We measured the change in conformational stability, Δ(ΔG), for hydrophobic mutants of four proteins: villin headpiece subdomain (VHP) with 36 residues, a surface protein from Borrelia burgdorferi (VlsE) with 341 residues, and two proteins previously studied in our laboratory, ribonucleases Sa and T1. We compared our results with those of previous studies and reached the following conclusions: (1) Hydrophobic interactions contribute less to the stability of a small protein, VHP (0.6 ± 0.3 kcal/mol per -CH2- group), than to the stability of a large protein, VlsE (1.6 ± 0.3 kcal/mol per -CH2- group). (2) Hydrophobic interactions make the major contribution to the stability of VHP (40 kcal/mol) and the major contributors are (in kilocalories per mole) Phe18 (3.9), Met13 (3.1), Phe7 (2.9), Phe11 (2.7), and Leu21 (2.7). (3) Based on the Δ(ΔG) values for 148 hydrophobic mutants in 13 proteins, burying a -CH2- group on folding contributes, on average, 1.1 ± 0.5 kcal/mol to protein stability. (4) The experimental Δ(ΔG) values for aliphatic side chains (Ala, Val, Ile, and Leu) are in good agreement with their ΔGtr values from water to cyclohexane. (5) For 22 proteins with 36 to 534 residues, hydrophobic interactions contribute 60 ± 4% and hydrogen bonds contribute 40 ± 4% to protein stability. (6) Conformational entropy contributes about 2.4 kcal/mol per residue to protein instability. The globular conformation of proteins is stabilized predominantly by hydrophobic interactions. 相似文献
988.
989.
Schuring RP Richardus JH Steyerberg EW Pahan D Faber WR Oskam L 《PLoS neglected tropical diseases》2008,2(8):e283
Background
To validate and update a prediction rule for estimating the risk of leprosy-related nerve function impairment (NFI).Methodology/Principal Findings
Prospective cohort using routinely collected data, in which we determined the discriminative ability of a previously published rule and an updated rule with a concordance statistic (c). Additional risk factors were analyzed with a Cox proportional hazards regression model. The population consisted of 1,037 leprosy patients newly diagnosed between 2002 and 2003 in the health care facilities of the Rural Health Program in Nilphamari and Rangpur districts in northwest Bangladesh. The primary outcome was the time until the start of treatment. An NFI event was defined as the decision to treat NFI with corticosteroids after diagnosis. NFI occurred in 115 patients (13%; 95% confidence interval 11%–16%). The original prediction rule had adequate discriminative ability (c = 0.79), but could be improved by substituting one predicting variable: ‘long-standing nerve function impairment at diagnosis’ by ‘anti-PGL-I antibodies’. The adjusted prediction rule was slightly better (c = 0.81) and identified more patients with NFI (80%) than the original prediction rule (72%).Conclusions/Significance
NFI can well be predicted by using the risk variables ‘leprosy classification’ and ‘anti-PGL-I antibodies’. The use of these two variables that do not include NFI offer the possibility of predicting NFI, even before it occurs for the first time. Surveillance beyond the treatment period can be targeted to those most likely to benefit from preventing permanent disabilities. 相似文献990.
Christiaan V. Henkel Ron P. Dirks Daniëlle L. de Wijze Yuki Minegishi Jun Aoyama Hans J. Jansen Ben Turner Bjarne Knudsen Martin Bundgaard Kenneth Lyneborg Hvam Marten Boetzer Walter Pirovano Finn-Arne Weltzien Sylvie Dufour Katsumi Tsukamoto Herman P. Spaink Guido E.E.J.M. van den Thillart 《Gene》2012
The Japanese eel is a much appreciated research object and very important for Asian aquaculture; however, its genomic resources are still limited. We have used a streamlined bioinformatics pipeline for the de novo assembly of the genome sequence of the Japanese eel from raw Illumina sequence reads. The total assembled genome has a size of 1.15 Gbp, which is divided over 323,776 scaffolds with an N50 of 52,849 bp, a minimum scaffold size of 200 bp and a maximum scaffold size of 1.14 Mbp. Direct comparison of a representative set of scaffolds revealed that all the Hox genes and their intergenic distances are almost perfectly conserved between the European and the Japanese eel. The first draft genome sequence of an organism strongly catalyzes research progress in multiple fields. Therefore, the Japanese eel genome sequence will provide a rich resource of data for all scientists working on this important fish species. 相似文献