全文获取类型
收费全文 | 2294篇 |
免费 | 11篇 |
国内免费 | 21篇 |
专业分类
系统科学 | 56篇 |
教育与普及 | 11篇 |
理论与方法论 | 42篇 |
现状及发展 | 268篇 |
研究方法 | 320篇 |
综合类 | 1400篇 |
自然研究 | 229篇 |
出版年
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 19篇 |
2017年 | 17篇 |
2016年 | 28篇 |
2015年 | 14篇 |
2014年 | 30篇 |
2013年 | 32篇 |
2012年 | 163篇 |
2011年 | 394篇 |
2010年 | 55篇 |
2009年 | 17篇 |
2008年 | 165篇 |
2007年 | 169篇 |
2006年 | 156篇 |
2005年 | 214篇 |
2004年 | 195篇 |
2003年 | 186篇 |
2002年 | 167篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1972年 | 5篇 |
1971年 | 7篇 |
1970年 | 8篇 |
1969年 | 7篇 |
1968年 | 7篇 |
1967年 | 9篇 |
1966年 | 7篇 |
排序方式: 共有2326条查询结果,搜索用时 15 毫秒
1.
James T. Ziegenfuss Jr. 《Systemic Practice and Action Research》1992,5(5):509-527
This paper discusses the use of the Kast and Rosenzweig systems and contingency model for teaching and practice in organizational analysis and planning, management policy, and organizational development. The need for an organizational model for graduate students and field-based managers and executives is identified. The model is presented beginning with the Kast and Rosenzweig work, with integration of research by Daft, Schein, Trist, Deal and Kennedy, Ackoff, Delbecq, and Mintzberg. The teaching and practice uses of the model in four areas are presented, including organizational analysis and planning, management policy making, and organizational development. In each area case examples of the use of the model in teaching and practice are presented. Needs for future research and implications for the use of the model are discussed. 相似文献
2.
3.
James W. McAllister 《Studies in history and philosophy of science》2005,36(2):403-410
This discussion note responds to objections by Twardy, Gardner, and Dowe to my earlier claim that empirical data sets are algorithmically incompressible. Twardy, Gardner, and Dowe hold that many empirical data sets are compressible by Minimum Message Length technique and offer this as evidence that these data sets are algorithmically compressible. I reply that the compression achieved by Minimum Message Length technique is different from algorithmic compression. I conclude that Twardy, Gardner, and Dowe fail to establish that empirical data sets are algorithmically compressible. 相似文献
4.
5.
Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner. 相似文献
6.
Structure,biosynthesis and functions of glycoprotein glycans 总被引:14,自引:0,他引:14
Eric G. Berger Eckhart Buddecke Johannis P. Kamerling Akira Kobata James C. Paulson Johannes F. G. Vliegenthart 《Cellular and molecular life sciences : CMLS》1982,38(10):1129-1162
Since the pioneering work on structure and function of heteroglycans compiled in the classical books edited by A. Gottschalk in 19721, there have been several promising developments in glycoconjugate research, as reviewed in this article.In Part 1, contributed by A. Kobata, current knowledge on heteroglycan structures is presented and representative examples taken from higher organisms are given. Part 2, written by J. F. G. Vliegenthart and J. P. Kamerling, covers the most important achievements in methodology: procedures to obtain pure glycans and to analyze their structures. Part 3, contributed by J. Paulson, is devoted to biosynthesis of glycans now describable as pathways since several of the glycosyltransferases have been isolated and analyzed for specificity. In Part 4, contributed by E. Buddecke, current knowledge on functional roles of glycans is presented. It will become apparent that the prerequisite for valid work either in biosynthetic or functional context depends on solid structural information. This is particularly true whenever glycosyltransferase reaction products are being analyzed, or glycans involved in biological functions are investigated. Although in past years, a great deal of important knowledge has been gathered by use of crude glycosidase or glycosyltransferase activities (a notable example is found in reference 2), one may now postulate that glycans implicated in biological reactions should be thoroughly analyzed.This review may familiarize newcomers with the field of glycoconjugate research with special emphasis on glycoprotein glycans. Glycolipids are not included in this article as they have recently been reviewed by S. I. Hakomori3. The reader is also referred to several excellent monographs4,5 and the Proceedings of the Glycoconjugate Symposia held biannually6–8. 相似文献
7.
泰国东北部柯叻府及邻区中-新生代木化石非常丰富并保存有完好的解剖构造,是探究热带植被历史、古气候演化以及古环境变迁等问题的重要实证材料.最近的野外调查和专题研究确认该地区中-新生代木化石11科19属约50个种或种级分类单元,分别隶属于裸子植物和被子植物两大分类群,其中有5科7属20种(包括未定种)为前人在泰国未曾报道的类型.当前木材化石群揭示出在中生代后期,泰国东北部热带针叶树植被以南洋杉科为主;在中新世-更新世时期,该地区主要发育落叶和常绿阔叶树植被,代表热带气候环境. 相似文献
8.
Chiang C Jacobsen JC Ernst C Hanscom C Heilbut A Blumenthal I Mills RE Kirby A Lindgren AM Rudiger SR McLaughlan CJ Bawden CS Reid SJ Faull RL Snell RG Hall IM Shen Y Ohsumi TK Borowsky ML Daly MJ Lee C Morton CC MacDonald ME Gusella JF Talkowski ME 《Nature genetics》2012,44(4):390-7, S1
We defined the genetic landscape of balanced chromosomal rearrangements at nucleotide resolution by sequencing 141 breakpoints from cytogenetically interpreted translocations and inversions. We confirm that the recently described phenomenon of 'chromothripsis' (massive chromosomal shattering and reorganization) is not unique to cancer cells but also occurs in the germline, where it can resolve to a relatively balanced state with frequent inversions. We detected a high incidence of complex rearrangements (19.2%) and substantially less reliance on microhomology (31%) than previously observed in benign copy-number variants (CNVs). We compared these results to experimentally generated DNA breakage-repair by sequencing seven transgenic animals, revealing extensive rearrangement of the transgene and host genome with similar complexity to human germline alterations. Inversion was the most common rearrangement, suggesting that a combined mechanism involving template switching and non-homologous repair mediates the formation of balanced complex rearrangements that are viable, stably replicated and transmitted unaltered to subsequent generations. 相似文献
9.
Mutations in the gene encoding pejvakin, a newly identified protein of the afferent auditory pathway, cause DFNB59 auditory neuropathy 总被引:5,自引:0,他引:5
Delmaghani S del Castillo FJ Michel V Leibovici M Aghaie A Ron U Van Laer L Ben-Tal N Van Camp G Weil D Langa F Lathrop M Avan P Petit C 《Nature genetics》2006,38(7):770-778
Auditory neuropathy is a particular type of hearing impairment in which neural transmission of the auditory signal is impaired, while cochlear outer hair cells remain functional. Here we report on DFNB59, a newly identified gene on chromosome 2q31.1-q31.3 mutated in four families segregating autosomal recessive auditory neuropathy. DFNB59 encodes pejvakin, a 352-residue protein. Pejvakin is a paralog of DFNA5, a protein of unknown function also involved in deafness. By immunohistofluorescence, pejvakin is detected in the cell bodies of neurons of the afferent auditory pathway. Furthermore, Dfnb59 knock-in mice, homozygous for the R183W variant identified in one DFNB59 family, show abnormal auditory brainstem responses indicative of neuronal dysfunction along the auditory pathway. Unlike previously described sensorineural deafness genes, all of which underlie cochlear cell pathologies, DFNB59 is the first human gene implicated in nonsyndromic deafness due to a neuronal defect. 相似文献
10.
Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms 总被引:15,自引:0,他引:15
Orr JC Fabry VJ Aumont O Bopp L Doney SC Feely RA Gnanadesikan A Gruber N Ishida A Joos F Key RM Lindsay K Maier-Reimer E Matear R Monfray P Mouchet A Najjar RG Plattner GK Rodgers KB Sabine CL Sarmiento JL Schlitzer R Slater RD Totterdell IJ Weirig MF Yamanaka Y Yool A 《Nature》2005,437(7059):681-686
Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms--such as corals and some plankton--will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean-carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously. 相似文献