全文获取类型
收费全文 | 3192篇 |
免费 | 12篇 |
国内免费 | 12篇 |
专业分类
系统科学 | 74篇 |
丛书文集 | 24篇 |
教育与普及 | 6篇 |
理论与方法论 | 5篇 |
现状及发展 | 1562篇 |
研究方法 | 133篇 |
综合类 | 1373篇 |
自然研究 | 39篇 |
出版年
2012年 | 43篇 |
2011年 | 74篇 |
2009年 | 18篇 |
2008年 | 58篇 |
2007年 | 60篇 |
2006年 | 55篇 |
2005年 | 55篇 |
2004年 | 85篇 |
2003年 | 57篇 |
2002年 | 50篇 |
2001年 | 102篇 |
2000年 | 98篇 |
1999年 | 66篇 |
1993年 | 21篇 |
1992年 | 83篇 |
1991年 | 46篇 |
1990年 | 43篇 |
1989年 | 37篇 |
1988年 | 26篇 |
1987年 | 40篇 |
1986年 | 46篇 |
1985年 | 51篇 |
1984年 | 58篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 45篇 |
1979年 | 96篇 |
1978年 | 61篇 |
1977年 | 80篇 |
1976年 | 53篇 |
1975年 | 53篇 |
1974年 | 103篇 |
1973年 | 86篇 |
1972年 | 75篇 |
1971年 | 83篇 |
1970年 | 117篇 |
1969年 | 104篇 |
1968年 | 113篇 |
1967年 | 97篇 |
1966年 | 106篇 |
1965年 | 74篇 |
1964年 | 31篇 |
1959年 | 27篇 |
1958年 | 49篇 |
1957年 | 39篇 |
1956年 | 44篇 |
1955年 | 31篇 |
1954年 | 25篇 |
1948年 | 32篇 |
排序方式: 共有3216条查询结果,搜索用时 15 毫秒
831.
832.
833.
We have investigated the reactivity of different human, rat and cat muscles to a monoclonal antibody directed against human alpha-cardiac myosin heavy chain. We have found that special fiber subpopulations of human masseter and extraocular muscles, as well as the bag fibers of human, rat and cat muscle spindles, were reactive to this antibody, indicating that these fibers expressed alpha-cardiac myosin heavy chain or a closely related isoform. This isomyosin was present in the spindle bag fibers at early fetal stages, whereas its expression in masseter and extraocular muscle fibers was not detected during the first 22 weeks of gestation. Our results add to the list of muscle proteins which are expressed in locations or at developmental stages other than those initially described, suggesting that a revision of the present nomenclature of the subgroups of myosin heavy chains might be considered in the future. 相似文献
834.
浅谈企业技术创新与信息资源开发 总被引:1,自引:1,他引:0
论述了信息在企业技术创新中的作用,并对企业技术创新信息需求的形成、内容特征及形式特征进行了分析,提出了强化信息资源开发的对策措施。 相似文献
835.
In hyperalgesic states, observed commonly as a major symptom of tissue inflammation or after central or peripheral nerve injury, non-noxious stimuli produce pain and noxious stimuli are perceived as more painful than usual. The mechanisms underlying the generation of hyperalgesia are not known. In patients with causalgia (burning pain and severe hyperalgesia after a nerve injury) activation of sympathetic post-ganglionic neurones or application of noradrenaline to painful skin exacerbates pain and hyperalgesia while sympathectomy may afford complete relief. One suggestion is that noradrenaline released from sympathetic post-ganglionic neurons increases the discharge of damaged small-diameter afferents by a direct action on the primary afferents. Here we present a new model for noradrenaline-sensitive hyperalgesia and demonstrate that the site of action of noradrenaline is not on the primary afferents but rather is presynaptic on the sympathetic post-ganglionic terminals. 相似文献
836.
837.
Molecular cloning and expression of cDNA for human granulocyte colony-stimulating factor 总被引:27,自引:0,他引:27
S Nagata M Tsuchiya S Asano Y Kaziro T Yamazaki O Yamamoto Y Hirata N Kubota M Oheda H Nomura 《Nature》1986,319(6052):415-418
Granulocyte colony-stimulating factor (G-CSF) is a member of the CSF family of hormone-like glycoproteins that regulate haematopoietic cell proliferation and differentiation, and G-CSF almost exclusively stimulates the colony formation of granulocytes from committed precursor cells in semi-solid agar culture. Recently, Nomura et al. have established a human squamous carcinoma cell line (designated CHU-2) from a human oral cavity tumour which produces large quantities of CSF constitutively, and the CSF produced by CHU-2 cells has been purified to homogeneity from the conditioned medium. We have now determined the partial amino-acid sequence of the purified G-CSF protein, and by using oligonucleotides as probes, have isolated several clones containing G-CSF complementary DNA from the cDNA library prepared with messenger RNA from CHU-2 cells. The complete nucleotide sequences of two of these cDNAs were determined and the expression of the cDNA in monkey COS cells gave rise to a protein showing authentic G-CSF activity. Furthermore, Southern hybridization analysis of DNA from normal leukocytes and CHU-2 cells suggests that the human genome contains only one gene for G-CSF and that some rearrangement has occurred within one of the alleles of the G-CSF gene in CHU-2 cells. 相似文献
838.
A new approach to isotonic agglomerative hierarchical clustering 总被引:1,自引:1,他引:0
Hierarchical clustering methods must be isotonic for the construction of ultrametric. We present a general strategy to widen
the class of isotonic methods implemented by agglomerative algorithms. At each step of the agglomeration we allow one of several
admissible pairs to be chosen. Then under mild assumptions an appropriate definition of admissibility guarantees isotony.
Moreover we consider the use of the new methods to compute locally optimal ultrametrics. Two examples demonstrate the ability
to define new agglomerative methods superior to their traditional competitors. 相似文献
839.
T Nakahata T Kobayashi A Ishiguro K Tsuji K Naganuma O Ando Y Yagi K Tadokoro T Akabane 《Nature》1986,324(6092):65-67
There are two phenotypically distinct subpopulations of mast cells in rodents: connective tissue-type mast cells (CTMC) and mucosal mast cells (MMC). These populations differ in their location, cell size, staining characteristics, ultrastructure, mediator content and T-cell dependency. Several investigators recently reported a further subclass of mast cells which arise when normal mouse haematopoietic cells are cultured with interleukin-3 (IL-3); IL-3 is an activity similar or identical to mast-cell growth factor, histamine-producing factor, or P-cell stimulating factor. These cultured mast cells are in many ways similar to MMC; they stain with Alcian blue but not safranin, contain chondroitin sulphate E proteoglycan rather than heparin proteoglycan and have relatively low histamine content, as do MMC. Although proliferation of MMC is known to be T-cell dependent in vivo and thought to be IL-3-dependent in vitro, the factors on which CTMC proliferation depends remain elusive. Here we show that mature CTMC purified from mouse peritoneal cells can proliferate in vitro in methylcellulose culture and maintain the appearance and function of CTMC. We also present evidence that mature CTMC cannot proliferate in the presence of pure IL-3 alone. 相似文献
840.
Summary A proteolysed form of fructose 1,6-bisphosphatase (Fru-P2ase) has been detected and characterized in human term placenta. The extract was found to contain very low levels of activity with an alkaline pH optimum. Western blotting demonstrated a polypeptide of Mr 26,000, instead of the subunit of Mr 36,000 observed in native mammalian Fru-P2ases. 相似文献