全文获取类型
收费全文 | 36561篇 |
免费 | 127篇 |
国内免费 | 121篇 |
专业分类
系统科学 | 190篇 |
丛书文集 | 792篇 |
教育与普及 | 90篇 |
理论与方法论 | 214篇 |
现状及发展 | 16034篇 |
研究方法 | 1500篇 |
综合类 | 17555篇 |
自然研究 | 434篇 |
出版年
2013年 | 210篇 |
2012年 | 477篇 |
2011年 | 962篇 |
2010年 | 217篇 |
2009年 | 181篇 |
2008年 | 636篇 |
2007年 | 649篇 |
2006年 | 675篇 |
2005年 | 672篇 |
2004年 | 706篇 |
2003年 | 646篇 |
2002年 | 646篇 |
2001年 | 1116篇 |
2000年 | 1040篇 |
1999年 | 717篇 |
1992年 | 637篇 |
1991年 | 537篇 |
1990年 | 551篇 |
1989年 | 552篇 |
1988年 | 550篇 |
1987年 | 569篇 |
1986年 | 571篇 |
1985年 | 701篇 |
1984年 | 571篇 |
1983年 | 461篇 |
1982年 | 405篇 |
1981年 | 435篇 |
1980年 | 529篇 |
1979年 | 1136篇 |
1978年 | 998篇 |
1977年 | 974篇 |
1976年 | 672篇 |
1975年 | 758篇 |
1974年 | 1074篇 |
1973年 | 911篇 |
1972年 | 950篇 |
1971年 | 1155篇 |
1970年 | 1523篇 |
1969年 | 1158篇 |
1968年 | 1086篇 |
1967年 | 1147篇 |
1966年 | 965篇 |
1965年 | 727篇 |
1959年 | 400篇 |
1958年 | 601篇 |
1957年 | 504篇 |
1956年 | 423篇 |
1955年 | 358篇 |
1954年 | 424篇 |
1948年 | 232篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
671.
672.
673.
674.
Predicting Recessions with Leading Indicators: Model Averaging and Selection over the Business Cycle 下载免费PDF全文
Travis J. Berge 《Journal of forecasting》2015,34(6):455-471
Four methods of model selection—equally weighted forecasts, Bayesian model‐averaged forecasts, and two models produced by the machine‐learning algorithm boosting—are applied to the problem of predicting business cycle turning points with a set of common macroeconomic variables. The methods address a fundamental problem faced by forecasters: the most useful model is simple but makes use of all relevant indicators. The results indicate that successful models of recession condition on different economic indicators at different forecast horizons. Predictors that describe real economic activity provide the clearest signal of recession at very short horizons. In contrast, signals from housing and financial markets produce the best forecasts at longer forecast horizons. A real‐time forecast experiment explores the predictability of the 2001 and 2007 recessions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
675.
The predominantly marine genus Schizopera Sars, 1905 has only two significant inland water species-flocks, one in the ancient African Lake Tanganyika and the other in subterranean waters of Western Australia. Discovery of Schizopera abei sp. nov. from several interstitial locations in the vicinity of the ancient Lake Biwa has wider implications for the study of morphological homoplasies in the genus, as well as for the study of freshwater invasions in harpacticoid copepods. The new Schizopera species belongs to a small group of congeners with a two-segmented endopod of the fourth leg, which used to be recognised as a separate genus, Schizoperopsis Apostolov, 1982. Our reconstructed phylogenies based on the mtCOI partial sequences suggest that this character probably evolved convergently in at least some Schizopera, thus rendering the genus Schizoperopsis polyphyletic. However, almost all basal nodes in our cladograms are weakly supported, which shows limitations of a single-gene approach for reconstructing phylogenetic relationships. The new species is the first member of its genus from Japanese inland waters, and it has no close relatives among extent congeners anywhere in the world. We speculate that its ancestor may have invaded Lake Biwa, and subsequently its surrounding subterranean waters, from brackish areas around central Japan, presumably during a period of high sea water level through its major outflow river. This discovery may provide further support for the hypothesis about the role of ancient lakes as biodiversity pumps for subterranean habitats.http://zoobank.org/urn:lsid:zoobank.org:pub:1F71F7AD-B7C8-4AD3-BE44-5E1BEE4E2AA8 相似文献
676.
Large intergenic non-coding RNA-RoR modulates reprogramming of human induced pluripotent stem cells 总被引:1,自引:0,他引:1
677.
Morelli G Song Y Mazzoni CJ Eppinger M Roumagnac P Wagner DM Feldkamp M Kusecek B Vogler AJ Li Y Cui Y Thomson NR Jombart T Leblois R Lichtner P Rahalison L Petersen JM Balloux F Keim P Wirth T Ravel J Yang R Carniel E Achtman M 《Nature genetics》2010,42(12):1140-1143
Plague is a pandemic human invasive disease caused by the bacterial agent Yersinia pestis. We here report a comparison of 17 whole genomes of Y. pestis isolates from global sources. We also screened a global collection of 286 Y. pestis isolates for 933 SNPs using Sequenom MassArray SNP typing. We conducted phylogenetic analyses on this sequence variation dataset, assigned isolates to populations based on maximum parsimony and, from these results, made inferences regarding historical transmission routes. Our phylogenetic analysis suggests that Y. pestis evolved in or near China and spread through multiple radiations to Europe, South America, Africa and Southeast Asia, leading to country-specific lineages that can be traced by lineage-specific SNPs. All 626 current isolates from the United States reflect one radiation, and 82 isolates from Madagascar represent a second radiation. Subsequent local microevolution of Y. pestis is marked by sequential, geographically specific SNPs. 相似文献
678.
The developmental dynamics of the maize leaf transcriptome 总被引:5,自引:0,他引:5
679.
Hüffmeier U Uebe S Ekici AB Bowes J Giardina E Korendowych E Juneblad K Apel M McManus R Ho P Bruce IN Ryan AW Behrens F Lascorz J Böhm B Traupe H Lohmann J Gieger C Wichmann HE Herold C Steffens M Klareskog L Wienker TF Fitzgerald O Alenius GM McHugh NJ Novelli G Burkhardt H Barton A Reis A 《Nature genetics》2010,42(11):996-999
Psoriatic arthritis (PsA) is an inflammatory joint disease that is distinct from other chronic arthritides and which is frequently accompanied by psoriasis vulgaris (PsV) and seronegativity for rheumatoid factor. We conducted a genome-wide association study in 609 German individuals with PsA (cases) and 990 controls with replication in 6 European cohorts including a total of 5,488 individuals. We replicated PsA associations at HLA-C and IL12B and identified a new association at TRAF3IP2 (rs13190932, P = 8.56 × 10?1?). TRAF3IP2 was also associated with PsV in a German cohort including 2,040 individuals (rs13190932, P = 1.95 × 10?3). Sequencing of the exons of TRAF3IP2 identified a coding variant (p.Asp10Asn, rs33980500) as the most significantly associated SNP (P = 1.13 × 10?2?, odds ratio = 1.95). Functional assays showed reduced binding of this TRAF3IP2 variant to TRAF6, suggesting altered modulation of immunoregulatory signals through altered TRAF interactions as a new and shared pathway for PsA and PsV. 相似文献
680.