全文获取类型
收费全文 | 41967篇 |
免费 | 67篇 |
国内免费 | 120篇 |
专业分类
系统科学 | 254篇 |
丛书文集 | 919篇 |
教育与普及 | 112篇 |
理论与方法论 | 245篇 |
现状及发展 | 18382篇 |
研究方法 | 1698篇 |
综合类 | 19948篇 |
自然研究 | 596篇 |
出版年
2013年 | 265篇 |
2012年 | 589篇 |
2011年 | 1212篇 |
2010年 | 245篇 |
2008年 | 735篇 |
2007年 | 762篇 |
2006年 | 801篇 |
2005年 | 804篇 |
2004年 | 777篇 |
2003年 | 763篇 |
2002年 | 757篇 |
2001年 | 1256篇 |
2000年 | 1153篇 |
1999年 | 795篇 |
1992年 | 740篇 |
1991年 | 600篇 |
1990年 | 644篇 |
1989年 | 616篇 |
1988年 | 619篇 |
1987年 | 656篇 |
1986年 | 643篇 |
1985年 | 785篇 |
1984年 | 654篇 |
1983年 | 538篇 |
1982年 | 469篇 |
1981年 | 451篇 |
1980年 | 589篇 |
1979年 | 1324篇 |
1978年 | 1107篇 |
1977年 | 1118篇 |
1976年 | 795篇 |
1975年 | 857篇 |
1974年 | 1251篇 |
1973年 | 1066篇 |
1972年 | 1091篇 |
1971年 | 1329篇 |
1970年 | 1744篇 |
1969年 | 1278篇 |
1968年 | 1219篇 |
1967年 | 1315篇 |
1966年 | 1101篇 |
1965年 | 797篇 |
1964年 | 200篇 |
1959年 | 471篇 |
1958年 | 707篇 |
1957年 | 592篇 |
1956年 | 501篇 |
1955年 | 419篇 |
1954年 | 484篇 |
1948年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
Enzymatic control of cell division in micro-organisms 总被引:1,自引:0,他引:1
NICKERSON WJ 《Nature》1948,162(4111):241-245
53.
Hong Zhang Kui Zhang Ying Mu Ning Yao Robert J. Sclabassi Mingui Sun 《自然科学进展(英文版)》2008,18(12):1507-1512
Image-based gait analysis as a means of biometric identification has attracted much research attention. Most of the existing methods focus on human identification, posture analysis and movement tracking. There have been few investigations on measuring the carried load based on the carrier's gait characteristics by automatic image processing. Nevertheless, this measurement is very useful in a number of applications, such as the study of the carried load on the postural development of children and adolescence. In this paper, we investigate how to automatically estimate the carried weight from a sequence of images. We present a method to extract human gait silhouette based on an observation that humans tend to minimize the energy during motion. We compute several angles of body leaning and determine the relationship of the carried weight, the leaning angles and the centroid location according to a human kinetic study. Our weight determination method has been verified successfully by experiments. 相似文献
54.
55.
The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchange (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p = 0.0001), smoking (p = 0.0231), and, to a small extent (p = 0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied. 相似文献
56.
57.
J A Martignetti A A Aqeel W A Sewairi C E Boumah M Kambouris S A Mayouf K V Sheth W A Eid O Dowling J Harris M J Glucksman S Bahabri B F Meyer R J Desnick 《Nature genetics》2001,28(3):261-265
The inherited osteolyses or 'vanishing bone' syndromes are a group of rare disorders of unknown etiology characterized by destruction and resorption of affected bones. The multicentric osteolyses are notable for interphalangeal joint erosions that mimic severe juvenile rheumatoid arthritis (OMIMs 166300, 259600, 259610 and 277950). We recently described an autosomal recessive form of multicentric osteolysis with carpal and tarsal resorption, crippling arthritic changes, marked osteoporosis, palmar and plantar subcutaneous nodules and distinctive facies in a number of consanguineous Saudi Arabian families. We localized the disease gene to 16q12-21 by using members of these families for a genome-wide search for homozygous-by-descent microsatellite markers. Haplotype analysis narrowed the critical region to a 1.2-cM region that spans the gene encoding MMP-2 (gelatinase A, collagenase type IV; (ref. 3). We detected no MMP2 enzymatic activity in the serum or fibroblasts of affected family members. We identified two family-specific homoallelic MMP2 mutations: R101H and Y244X. The nonsense mutation effects a deletion of the substrate-binding and catalytic sites and the fibronectin type II-like and hemopexin/TIMP2 binding domains. Based on molecular modeling, the missense mutation disrupts hydrogen bond formation within the highly conserved prodomain adjacent to the catalytic zinc ion. 相似文献
58.
Induction of hemopoietic chimerism in the caprine fetus by intraperitoneal injection of fetal liver cells 总被引:1,自引:0,他引:1
R. D. Pearce D. Kiehm D. T. Armstrong P. B. Little J. W. Callahan L. R. Klunder J. T. R. Clarke 《Cellular and molecular life sciences : CMLS》1989,45(3):307-308
Summary Intraperitoneal injection of allogeneic liver cells from 43-day-old male fetuses into normal 60-day female goat fetuses resulted in persistent hemopoietic chimerism in surviving recipients without clinical evidence of graft-versus-host disease. Transplantation of normal fetal liver cells into preimmunocompetent goat fetuses affected with -D-mannosidosis may provide an alternative strategy for evaluating hemopoietic stem cell transplantation in the treatment of human lysosomal storage diseases. 相似文献
59.
P. Levy G. Cherqui A. Robert D. Wicek J. Picard 《Cellular and molecular life sciences : CMLS》1989,45(6):588-591
Summary During the spontaneous differentiation (day 5 to day 15 of the culture) of Caco-2 cells, the sulfation of cell layer glycosaminoglycans increased, whereas protein kinase C activity was concomitantly redistributed from the membrane to the cytosol. The protein kinase C activators, 4-phorbol 12-myristate, 13-acetate and 1,2-dioctanoyl-glycerol inhibited glycosaminoglycan sulfation. By contrast, 4-phorbol 12, 13 didecanoate was ineffective.These results suggest that membrane-bound PKC may exert a modulatory effect on glycosaminoglycan sulfation, and this effect is gradually attenuated as Caco-2 cell differentiation progresses. 相似文献
60.
C. Gianoulakis 《Cellular and molecular life sciences : CMLS》1989,45(5):428-435
Summary Alcoholism and alcohol abuse are serious health problems. Alcohol is known to influence the activity of a number of biological systems, for example the hormonal and neuronal systems. One of the biological systems whose activity is greatly influenced by alcohol is the endogenous opiate system. Alcohol modifies the function of both opiate receptors and opioid peptides. In fact it has been proposed that many of the effects of ethanol are mediated by its effects on the endogenous opiate system. This review will present results from various laboratories on the effects of acute and chronic ethanol treatments on various species, and on the release, biosynthesis and post-translational processing of the endorphins, enkephalins and dynorphins, the three known families of endogenous opioid peptides. Furthermore, the effect of acute and chronic ethanol consumption on the -endorphin system in man, and the possible implications of the functional activity of the endogenous opiate system for the genetic predisposition to alcoholism will be discussed. 相似文献