全文获取类型
收费全文 | 491999篇 |
免费 | 59288篇 |
国内免费 | 287篇 |
出版年
2018年 | 4668篇 |
2017年 | 4381篇 |
2016年 | 6429篇 |
2015年 | 9057篇 |
2014年 | 10199篇 |
2013年 | 14705篇 |
2012年 | 17703篇 |
2011年 | 18125篇 |
2010年 | 11482篇 |
2009年 | 10233篇 |
2008年 | 15672篇 |
2007年 | 16210篇 |
2006年 | 14726篇 |
2005年 | 14329篇 |
2004年 | 14012篇 |
2003年 | 13294篇 |
2002年 | 12798篇 |
2001年 | 22861篇 |
2000年 | 23126篇 |
1999年 | 18196篇 |
1998年 | 6659篇 |
1997年 | 6816篇 |
1996年 | 6707篇 |
1995年 | 6060篇 |
1994年 | 6133篇 |
1993年 | 5900篇 |
1992年 | 14108篇 |
1991年 | 13341篇 |
1990年 | 13006篇 |
1989年 | 12847篇 |
1988年 | 11485篇 |
1987年 | 11119篇 |
1986年 | 10163篇 |
1985年 | 10008篇 |
1984年 | 8594篇 |
1983年 | 7431篇 |
1982年 | 5853篇 |
1981年 | 5314篇 |
1980年 | 4933篇 |
1979年 | 7970篇 |
1978年 | 6192篇 |
1977年 | 5691篇 |
1976年 | 5325篇 |
1975年 | 5684篇 |
1974年 | 6055篇 |
1973年 | 5895篇 |
1972年 | 5259篇 |
1971年 | 4916篇 |
1970年 | 4064篇 |
1969年 | 3996篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Urease was immobilized on O-alkylated nylon tubes coated with polyaminated derivatives of starch or dextran. The specific activity of the enzyme coil and the relative stability of the immobilized enzyme, compared with immobilized urease derived from other nylon tube modifications, were enhanced. Also, the nonspecific binding of urease to O-alkylated nylon tubes was virtually eliminated by the coating process. 相似文献
994.
995.
Sporadic (less than regular weekly) coital activity is associated with a particular type of infertility—the short hyperthermic (luteal) phase. This preliminary report is the first suggestion that a reduced frequency of human sexual activity might, itself, be associated with subfertile reproductive function. 相似文献
996.
997.
998.
Fenestrated capillaries in the ventral sebaceous gland of the Djungarian hamster, Phodopus sungorus 总被引:1,自引:0,他引:1
The ventral sebaceous gland of the Djungarian hamster is a macroscopically visible organ situated in the midventral area of the abdominal wall. It consists of densely packed acini arranged in lobules with common excretory ducts. The rich vascular network of the gland is characterized by fenestrated capillaries. Fenestrated endothelium has not yet been reported as a characteristic and regular finding within sebaceous glands. Results are discussed with regard to proliferation rate of sebocytes and the demand of fluid and nutrient supply. 相似文献
999.
A mutant of Aspergillus nidulans, designated nuv11, has been isolated as hypersensitive to the monofunctional alkylating agent MNNG and the quasi-UV-mimetic mutagen 4-NQO. The mutation was recessive, resulting from mutation of a single gene which mapped to chromosome IV, and was non-allelic to the previously characterised repair-deficient mutations uvsB and uvsH which are also located on this linkage group. The nuv11 mutation results in slow growth, deficient intragenic and intergenic meiotic recombination, increased spontaneous chromosome instability, and increased intragenic and intergenic mitotic recombination in homozygous diploids. By screening a wild-type gene bank of A nidulans, a clone (pNUV11A40) has been isolated which complements the nuv11 mutation, restoring wild-type responses to both MNNG and 4-NQO. 相似文献
1000.
V Cavallari A Maiorana M C Maiorana R A Fano S Scimone G P Trentini 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》1991,13(2):123-131
A morphometric study of subcellular structures in human primary breast tumors (of the ductal infiltrating type) and their synchronous lymph node metastases was carried out using planimetry and stereology. Each primary neoplasm was compared separately with its axillary metastatic growth in order to detect differences in the quantitative estimates of their subcellular components. A set of 24 morphometric parameters was used to quantitatively describe each neoplastic cell profile. Although some subcellular parameters showed significant differences between the cells of a primary tumor and its metastases, no parameter was found to be consistently altered in all cases. No consistent increase or decrease in the values of the affected parameters was observed in the metastases. More than being due to the expression of a biologically variant (more-or-less differentiated) metastatic phenotype, the differences in stereologic parameters detected in metastatic cells appear to reflect the existence of different functional states of the same cell type. 相似文献