全文获取类型
收费全文 | 1041篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 19篇 |
教育与普及 | 1篇 |
理论与方法论 | 18篇 |
现状及发展 | 365篇 |
研究方法 | 169篇 |
综合类 | 464篇 |
自然研究 | 6篇 |
出版年
2020年 | 5篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2014年 | 13篇 |
2013年 | 10篇 |
2012年 | 58篇 |
2011年 | 73篇 |
2010年 | 26篇 |
2009年 | 6篇 |
2008年 | 40篇 |
2007年 | 53篇 |
2006年 | 55篇 |
2005年 | 51篇 |
2004年 | 28篇 |
2003年 | 30篇 |
2002年 | 41篇 |
2001年 | 34篇 |
2000年 | 41篇 |
1999年 | 35篇 |
1997年 | 5篇 |
1992年 | 31篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1972年 | 14篇 |
1971年 | 15篇 |
1970年 | 14篇 |
1969年 | 12篇 |
1968年 | 9篇 |
1967年 | 11篇 |
1966年 | 8篇 |
1964年 | 6篇 |
1956年 | 6篇 |
排序方式: 共有1042条查询结果,搜索用时 31 毫秒
121.
陆林根 《系统工程与电子技术》1994,(12)
为了在地杂波中检出运动目标的信号,雷达采用动目标处理器,它由滤波器或滤波器组组成。本文主要叙述这些滤波器的设计,提出了许多对实际雷达有使用价值的设计方法。此方法的主要内容是滤波器系数的选择、系统改善因子的计算。本文还附有实际计算的例子。 相似文献
122.
N de Wind M Dekker N Claij L Jansen Y van Klink M Radman G Riggins M van der Valk K van't Wout H te Riele 《Nature genetics》1999,23(3):359-362
Cancer predisposition in hereditary non-polyposis colon cancer (HNPCC) is caused by defects in DNA mismatch repair (MMR). Mismatch recognition is attributed to two heterodimeric protein complexes: MutSalpha (refs 2, 3, 4, 5), a dimer of MutS homologues MSH2 and MSH6; and MutSbeta (refs 2,7), a dimer of MSH2 and MSH3. These complexes have specific and redundant mismatch recognition capacity. Whereas MSH2 deficiency ablates the activity of both dimers, causing strong cancer predisposition in mice and men, loss of MSH3 or MSH6 (also known as GTBP) function causes a partial MMR defect. This may explain the rarity of MSH6 and absence of MSH3 germline mutations in HNPCC families. To test this, we have inactivated the mouse genes Msh3 (formerly Rep3 ) and Msh6 (formerly Gtmbp). Msh6-deficient mice were prone to cancer; most animals developed lymphomas or epithelial tumours originating from the skin and uterus but only rarely from the intestine. Msh3 deficiency did not cause cancer predisposition, but in an Msh6 -deficient background, loss of Msh3 accelerated intestinal tumorigenesis. Lymphomagenesis was not affected. Furthermore, mismatch-directed anti-recombination and sensitivity to methylating agents required Msh2 and Msh6, but not Msh3. Thus, loss of MMR functions specific to Msh2/Msh6 is sufficient for lymphoma development in mice, whereas predisposition to intestinal cancer requires loss of function of both Msh2/Msh6 and Msh2/Msh3. 相似文献
123.
124.
Radiation carcinogenesis in experimental animals 总被引:1,自引:0,他引:1
Exposure of man to relatively high doses of ionizing radiation is generally restricted to accidental situations, with very limited knowledge about the actual doses received. Animal experiments can be performed under standardized and controlled conditions and can provide information on the dose-response relationships for radiation carcinogenesis. The risk of inducing neoplastic late effects after total-body irradiation with relatively high doses has been demonstrated for larger animals, such as monkeys and dogs. The bone marrow, the mammary glands and the lungs are among the tissues with the highest susceptibility for radiation carcinogenesis. Experimental results on tumour induction in rodents are summarized with emphasis on the effectiveness in dependence on radiation quality and fractionation or dose rate. 相似文献
125.
S M Sisodiya S L Free K A Williamson T N Mitchell C Willis J M Stevens B E Kendall S D Shorvon I M Hanson A T Moore V van Heyningen 《Nature genetics》2001,28(3):214-216
PAX6 is widely expressed in the central nervous system. Heterozygous PAX6 mutations in human aniridia cause defects that would seem to be confined to the eye. Magnetic resonance imaging (MRI) and smell testing reveal the absence or hypoplasia of the anterior commissure and reduced olfaction in a large proportion of aniridia cases, which shows that PAX6 haploinsuffiency causes more widespread human neuro developmental anomalies. 相似文献
126.
John P. van Gigch 《Systemic Practice and Action Research》1997,10(4):381-394
We outline an epistemology to resolve dilemmas among conflicting imperatives which arise in management situations involving action programs which are “useful” economically and technically but which, at the same time, must satisfy, among others, aesthetic, ethical, and legal requirements. These “situations” occur in problem domains such as management science, environmental management, conservation management (the science devoted to the protection and preservation of our cultural and historical heritage), urban planning, government administration, and the like. Basically, these actions programs are designed to “improve the state of the real world” and take into account the inevitable conflicts and tradeoffs which inhibit maximization of objectives. In the end, the epistemological framework which is proposed leads to the formulation of a methodology to reconcile the economic, scientific, political, legal, ethical, epistemological, and aesthetic imperatives, in the context of a strategic and pragmatic framework. 相似文献
127.
128.
G W van Eijk 《Experientia》1973,29(5):522-523
129.
T R Koiter G C van der Schaaf-Verdonk S Broers N Pols-Valkhof G A Schuiling 《Experientia》1986,42(3):304-307
In ovariectomized rats the desensitization of the LH cells in vivo, which develops during constant rate infusion of LHRH, 1) does not depend on a concomitant depletion of the pituitary LH stores, 2) proceeds normally when the hypothalamo-pituitary connection has been severed and 3) is a process in which LH itself is not involved. 相似文献
130.
Summary In the brain wall of different vertebrate species, ependymal cells of different type occur. These cells possess protuberances which protrude into the ventricle.Although cytologically these structures are all variations of one theme, they must at present be interpreted in different ways as regards function.Probably these cell types form a complex system for the regulation of the cerebrospinal fluid. It remains possible that one or more of these cell types act as light receptors. 相似文献