全文获取类型
收费全文 | 1740798篇 |
免费 | 140491篇 |
国内免费 | 3245篇 |
专业分类
耳鼻咽喉 | 23035篇 |
儿科学 | 56539篇 |
妇产科学 | 48795篇 |
基础医学 | 246630篇 |
口腔科学 | 50522篇 |
临床医学 | 154496篇 |
内科学 | 343838篇 |
皮肤病学 | 36855篇 |
神经病学 | 143697篇 |
特种医学 | 70286篇 |
外国民族医学 | 482篇 |
外科学 | 264278篇 |
综合类 | 41405篇 |
现状与发展 | 5篇 |
一般理论 | 675篇 |
预防医学 | 133175篇 |
眼科学 | 39432篇 |
药学 | 130867篇 |
5篇 | |
中国医学 | 3192篇 |
肿瘤学 | 96325篇 |
出版年
2018年 | 17837篇 |
2017年 | 14071篇 |
2016年 | 15686篇 |
2015年 | 18182篇 |
2014年 | 25146篇 |
2013年 | 37462篇 |
2012年 | 51878篇 |
2011年 | 54719篇 |
2010年 | 32068篇 |
2009年 | 30806篇 |
2008年 | 52159篇 |
2007年 | 55024篇 |
2006年 | 55319篇 |
2005年 | 54119篇 |
2004年 | 53019篇 |
2003年 | 50608篇 |
2002年 | 49310篇 |
2001年 | 77180篇 |
2000年 | 79457篇 |
1999年 | 67951篇 |
1998年 | 19631篇 |
1997年 | 17833篇 |
1996年 | 17584篇 |
1995年 | 17177篇 |
1994年 | 16095篇 |
1993年 | 15228篇 |
1992年 | 56177篇 |
1991年 | 54528篇 |
1990年 | 53163篇 |
1989年 | 51415篇 |
1988年 | 47734篇 |
1987年 | 47145篇 |
1986年 | 44769篇 |
1985年 | 43363篇 |
1984年 | 32637篇 |
1983年 | 28113篇 |
1982年 | 16840篇 |
1981年 | 15070篇 |
1980年 | 14116篇 |
1979年 | 30820篇 |
1978年 | 21394篇 |
1977年 | 18152篇 |
1976年 | 17000篇 |
1975年 | 17845篇 |
1974年 | 21732篇 |
1973年 | 20916篇 |
1972年 | 19045篇 |
1971年 | 17921篇 |
1970年 | 16451篇 |
1969年 | 15389篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Juin Fok-Seang Linda C. Smith-Thomas Sally Meiners Elizabeth Muir Jian-Sheng Du Elizabeth Housden Alan R. Johnson Andreas Faissner Herbert M. Geller Roger J. Keynes John H. Rogers James W. Fawcett 《Brain research》1995,689(2):207
The adult mammalian central nervous system (CNS) lacks the capacity to support axonal regeneration. There is increasing evidence to suggest that astrocytes, the major glial population in the CNS, may possess both axon-growth promoting and axon-growth inhibitory properties and the latter may contribute to the poor regenerative capacity of the CNS. In order to examine the molecular differences between axon-growth permissive and axon-growth inhibitory astrocytes, a panel of astrocyte cell lines exhibiting a range of axon-growth promoting properties was generated and analysed. No clear correlation was found between the axon-growth promoting properties of these astrocyte cell lines with: (i) the expression of known neurite-outgrowth promoting molecules such as laminin, fibronectin andN-cadherin; (ii) the expression of known inhibitory molecules such tenascin and chondroitin sulphate proteoglycan; (iii) plasminogen activator and plasminogen activator inhibitor activity; and (iv) growth cone collapsing activity. EM studies on aggregates formed from astrocyte cell lines, however, revealed the presence of an abundance of extracellular matrix material associated with the more inhibitory astrocyte cell lines. When matrix deposited by astrocyte cell lines was assessed for axon-growth promoting activity, matrix from permissive lines was found to be a good substrate, whereas matrix from the inhibitory astrocyte lines was a poor substrate for neuritic growth. Our findings, taken together, suggest that the functional differences between the permissive and the inhibitory astrocyte cell lines reside largely with the ECM. 相似文献
232.
Xu Dai-gen He Han-zhen Zhang Guo-gao B. Gansewendt H. Peter H. M. Bolt 《华中科技大学学报(医学英德文版)》1993,13(2):100-104
Monohalogenated methanes (methyl chloride, methyl bromide and methyl iodide) are mutagenic and carcinogenic. The possible mechanism of these effects, DNA methylation, was studied. DNA adducts from orgnas of F344 rats exposed to these chemicals were separated and identified with high performance liquid chromatography (HPLC) and gaschro-matography/massspectrometry (GC/ MS). DNA adducts, 7-methylguanine (7-MeG) and O6-Methylguanine(08-MeG), incorporation of14C into de novo synthesis of nucleobases could be observed in enzymatic DNA hydrolysates by HPLC and determination of the radioactivity in the fractions. The formation of DNA add,ue,ts in the studied organs was only quantitatively different. The formation of O6-MeG was further pioved by analysing the acidic hydrolysates using HPLC with non-radioactive O6MeG as internal standard. 7-MeG and 3-MeA were identified with GC/MS analysis. 相似文献
233.
Excessive zinc ingestion. A reversible cause of sideroblastic anemia and bone marrow depression 总被引:2,自引:0,他引:2
Two patients with sideroblastic anemia secondary to zinc-induced copper deficiency absorbed excess zinc secondary to oral ingestion. The source of excess zinc was a zinc supplement in one case; in the other, ingested coins. In each case, the sideroblastic anemia was corrected promptly after removal of the source of excess zinc. These two cases emphasize the importance of recognizing this clinical entity, since the myelodysplastic features are completely reversible. 相似文献
234.
235.
E R Wald 《The Journal of family practice》1988,26(4):367-368
236.
237.
Oil-emulsified (OE) and aqueous (Aq) vaccines were prepared with the same batch of inactivated A24 8345 foot and mouth disease virus (FMDV). Calves born to vaccinated dams did not respond to the Aq vaccine 30 or 90 days post partum. When the OE vaccine was used on a similar group of calves, no responses were elicited up to 21 days post partum. However, calves 30 or more days old responded like adult cattle to the OE vaccine. When the OE vaccine was used in colostral antibody-free calves 3-30 days old, all animals showed good antibody responses but, in calves vaccinated 3 or 7 days post partum, antibodies were detectable only after a considerable period of time. Our results show that both passively acquired colostral antibodies and age are important in the response of very young calves to FMDV oil vaccines. From a practical point of view, in endemic areas where adult cattle are periodically vaccinated, vaccination of calves between 30 and 60 days post partum with OE vaccines would lead to high levels of herd protection. 相似文献
238.
R. P. Heaney T. M. Zizic I. Fogelman W. P. Olszynski P. Geusens C. Kasibhatla N. Alsayed G. Isaia M. W. Davie C. H. Chesnut III 《Osteoporosis international》2002,13(6):501-505
Risedronate treatment reduces the risk of vertebral fracture in women with existing vertebral fractures, but its efficacy
in prevention of the first vertebral fracture in women with osteoporosis but without vertebral fractures has not been determined.
We examined the risk of first vertebral fracture in postmenopausal women who were enrolled in four placebo-controlled clinical
trials of risedronate and who had low lumbar spine bone mineral density (BMD) (mean T-score =–3.3) and no vertebral fractures at baseline. Subjects received risedronate 5 mg (n= 328) or placebo (n= 312) daily for up to 3 years; all subjects were given calcium (1000 mg daily), as well as vitamin D supplementation (up
to 500 IU daily) if baseline serum 25-hydroxyvitamin D levels were low. The incidence of first vertebral fracture was 9.4%
in the women treated with placebo and 2.6% in those treated with risedronate 5 mg (risk reduction of 75%, 95% confidence interval
37% to 90%; P= 0.002). The number of patients who would need to be treated to prevent one new vertebral fracture is 15. When subjects were
stratified by age, similar significant reductions were observed in patients with a mean age of 64 years (risk reduction of
70%, 95% CI 8% to 90%; P= 0.030) and in those with a mean age of 76 years (risk reduction of 80%, 95% CI 7% to 96%; P= 0.024). Risedronate treatment therefore significantly reduces the risk of first vertebral fracture in postmenopausal women
with osteoporosis, with a similar magnitude of effect early and late after the menopause.
Received: 12 September 2001 / Accepted: 11 December 2001 相似文献
239.