首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   17391篇
  免费   43篇
  国内免费   54篇
系统科学   255篇
丛书文集   444篇
教育与普及   36篇
理论与方法论   50篇
现状及发展   7992篇
研究方法   740篇
综合类   7811篇
自然研究   160篇
  2012年   219篇
  2011年   439篇
  2010年   101篇
  2009年   95篇
  2008年   276篇
  2007年   351篇
  2006年   299篇
  2005年   305篇
  2004年   277篇
  2003年   331篇
  2002年   264篇
  2001年   614篇
  2000年   612篇
  1999年   347篇
  1992年   330篇
  1991年   256篇
  1990年   299篇
  1989年   272篇
  1988年   262篇
  1987年   276篇
  1986年   284篇
  1985年   338篇
  1984年   242篇
  1983年   219篇
  1982年   201篇
  1981年   238篇
  1980年   261篇
  1979年   574篇
  1978年   464篇
  1977年   469篇
  1976年   351篇
  1975年   376篇
  1974年   586篇
  1973年   459篇
  1972年   413篇
  1971年   517篇
  1970年   658篇
  1969年   573篇
  1968年   494篇
  1967年   529篇
  1966年   439篇
  1965年   331篇
  1964年   88篇
  1959年   198篇
  1958年   293篇
  1957年   192篇
  1956年   172篇
  1955年   167篇
  1954年   159篇
  1948年   87篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Summary Assays of 8 synthetic analogues of human calcitonin in rats showed that their hypocalcaemic activity was drastically reduced by deletion of the C-terminal amide group, chain-shortening or opening of the disulphide ring, but unaffected or enhanced by modification of the N-terminal amino group.

II. vgl.R. Maier, B. Kamber, B. Riniker andW. Rittel, Hormon. Metab. Res.7, 511 (1975).

Die hier verwendete, abgekürzte Schreibweise für Peptide folgt den Empfehlungen der IUPAC-IUB Kommission für Biochemische Nomenklatur, J.B.C.247, 977 (1972). Weitere Abkürzungen: HCT, Human-Calcitonin; PCT, Schweinecalcitonin; Bmp, -Mercaptopropionsäure (Desaminocystein); NMet, Normethionin (S-Methylcystein); -OMe, Methylester.  相似文献   
102.
Summary 4-isothiocyanato-4-nitrodiphenylamine was found to possess activity against intestinal nematodes in mice, against schistosomes in various hosts including primates and against two filarial species in the mongolian jird. Upon administration in a single oral dose it is equally effective againstS. haematobium, S. mansoni andS. japonicum.  相似文献   
103.
104.
Associations with ants, termed myrmecophily, are widespread in the butterfly family Lycaenidae and range from mere co-existence to more or less specific mutualistic or even parasitic interactions. Secretions of specialized epidermal glands are crucial for mediating the interactions. Transfer of nutrients (carbohydrates, amino acids) from butterfly larvae to ants plays a major role, but manipulative communication with the help of odour signals is also involved. By means of myrmecophily, lycaenid butterflies largely escape ant predation, and certain species gain protection through attendant ants or achieve developmental benefits from ant-attendance. Benefits to the ants range from minimal to substantial food rewards. While most lycaenid species maintain facultative relationships with a variety of ant genera, highly specific and obligatory associations have convergently evolved in a number of butterfly lineages. As a corollary, communication systems are largely unspecific in the former, but may be highly specialized in the latter. The sophisticated communication between obligate myrmecophiles and their host ants is tightly connected with the evolutionary rise of specialized life-cycles and thus is a source of augmenting diversity within the butterflies.  相似文献   
105.
Microarray analysis has become a widely used tool for the generation of gene expression data on a genomic scale. Although many significant results have been derived from microarray studies, one limitation has been the lack of standards for presenting and exchanging such data. Here we present a proposal, the Minimum Information About a Microarray Experiment (MIAME), that describes the minimum information required to ensure that microarray data can be easily interpreted and that results derived from its analysis can be independently verified. The ultimate goal of this work is to establish a standard for recording and reporting microarray-based gene expression data, which will in turn facilitate the establishment of databases and public repositories and enable the development of data analysis tools. With respect to MIAME, we concentrate on defining the content and structure of the necessary information rather than the technical format for capturing it.  相似文献   
106.
Nuclear transfer into mouse zygotes   总被引:6,自引:0,他引:6  
  相似文献   
107.
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   
108.
109.
110.
The long-term energy demand in China and the-Chinese share in global CO2 emission are forecasted on the basis of scenarios of population growth and economy development up to 2050 proposed in view of the interaction of energy, economy, environment and social development. The total energy demand in 2050 will reach 4.4~ 5.4 billion tce. It is shown in energy supply analysis that coal is China's major energy in primary energy supply. The share of CO2 emission in the future Chinese energy system will be out of proportion to its energy consumption share because of the high persentage of coal to be consumed. It will reach about 27%. The nuclear option which would replace 30.7% of coal in the total primary energy supply will reduce the share by 9.8%. So the policy considerations on the future Chinese energy system is of great importance to the global CO2 issues.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号