全文获取类型
收费全文 | 767684篇 |
免费 | 87193篇 |
国内免费 | 512篇 |
专业分类
855389篇 |
出版年
2018年 | 6676篇 |
2016年 | 9286篇 |
2015年 | 12195篇 |
2014年 | 14438篇 |
2013年 | 21039篇 |
2012年 | 23374篇 |
2011年 | 23576篇 |
2010年 | 16105篇 |
2009年 | 14902篇 |
2008年 | 20944篇 |
2007年 | 21625篇 |
2006年 | 20274篇 |
2005年 | 19697篇 |
2004年 | 19380篇 |
2003年 | 18828篇 |
2002年 | 18080篇 |
2001年 | 35504篇 |
2000年 | 35462篇 |
1999年 | 28125篇 |
1998年 | 9494篇 |
1997年 | 10124篇 |
1996年 | 9526篇 |
1995年 | 8826篇 |
1994年 | 8653篇 |
1993年 | 8643篇 |
1992年 | 22973篇 |
1991年 | 22196篇 |
1990年 | 21469篇 |
1989年 | 21027篇 |
1988年 | 19469篇 |
1987年 | 18444篇 |
1986年 | 17281篇 |
1985年 | 17194篇 |
1984年 | 14263篇 |
1983年 | 12280篇 |
1982年 | 9399篇 |
1981年 | 8686篇 |
1980年 | 8098篇 |
1979年 | 13826篇 |
1978年 | 10707篇 |
1977年 | 10049篇 |
1976年 | 9243篇 |
1975年 | 10118篇 |
1974年 | 11079篇 |
1973年 | 10784篇 |
1972年 | 9971篇 |
1971年 | 9041篇 |
1970年 | 7826篇 |
1969年 | 7606篇 |
1968年 | 7021篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
J W Costerton 《Canadian journal of microbiology》1988,34(4):513-521
912.
W J Theuvenet T Nolthenius-Puylaert Z L Giedrojc Juraha J M Borghouts R van Twisk 《Plastic and reconstructive surgery》1984,74(4):539-543
Idiopathic calcinosis of the scrotum is a rare disease that may cause massive deformation of the scrotal wall. The first patient we present was also known to have neurofibromatosis. In the second patient we describe, nodules of idiopathic calcinosis of the scrotum were seen with walls that evidenced no epithelial lining, as well as calcification in epithelial cysts. At present, the only possible treatment is excision, and we excised the afflicted skin without problems in primary wound closure. 相似文献
913.
914.
Genomic DNA isolated from 20 horses was digested with up to six restriction endonucleases and subjected to southern blot hybridization analysis using various human class II alpha- and beta-chain cDNA probes. A high degree of restriction fragment length polymorphism (RFLP) was found for the DQ alpha, DP beta, DQ beta and DR beta probes, about 20 polymorphic bands being detected for each. DR alpha showed 2-4 polymorphic bands, whereas no evidence for DP alpha-like genes was found. A number of correlations of RFLPs with individual alloantisera were apparent. 相似文献
915.
916.
An I125 radioimmunoassay (RIA) has been developed for the measurement of plasma and tissue epinephrine (E) and norepinephrine (NE). The assay utilizes an antibody which specifically binds metanephrine. E and NE are detected by conversion to metanephrine with the enzymes catechol-0-methyltransferase and phenylethanol-amine-N-methyltransferase. The assay is very specific and will allow the measurement of E and NE in less than 500 μl of normal human plasma. E and NE concentrations were determined by both the RIA and a radioenzymatic assay in canine, human and rat biologic samples. The correlation coefficients between the two assays were .962 for E and .956 for NE. The RIA is sensitive, specific, precise and significantly less costly and time consuming than present radioenzymatic methods. 相似文献
917.
In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time. 相似文献
918.
One hundred and forty-four isolates of dairy origin were identified using a number of commercially available test kits. Agreement between these kits was acceptable for assignment of isolates to genera, but there was some variation between the kits for the identification of the isolates at specific level. The reasons for these variations are discussed. In terms of cost, ease of performance and accuracy, the identification systems manufactured by Roche Products Ltd (viz. the Oxi/Ferm tube and the Enterotube) are considered to be the best suited to the routine identification of dairy micro-organisms. 相似文献
919.
D B Snead A Weltman J Y Weltman W S Evans J D Veldhuis M M Varma C D Teates E A Dowling A D Rogol 《Journal of applied physiology》1992,72(6):2149-2156
We examined the relationships among reproductive hormone concentrations and bone mineral density (BMD) in 43 women runners classified as eumenorrheic (n = 24), oligomenorrheic (n = 8), or amenorrheic (n = 11). Results were compared with a eumenorrheic nonrunner control group (n = 11). Serum 17 beta-estradiol, progesterone, and dehydroepiandrosterone sulfate concentrations were determined in daily blood samples for 21 days, and integrated concentrations (areas under the curve) were calculated. BMD was assessed at the lumbar spine and proximal femur by dual-photon absorptiometry. As expected, 17 beta-estradiol, progesterone, and lumbar spine BMD were higher in the control and eumenorrheic runner groups than in the oligomenorrheic and amenorrheic runner groups (P less than 0.05). Progesterone concentration was significantly correlated with lumbar spine BMD in the eumenorrheic runners (r = 0.61). None of the steroid hormones was significantly related to BMD in the oligomenorrheic/amenorrheic group. The present data suggest that circulating levels of gonadal steroid hormones affect axial BMD in eumenorrheic runners. 相似文献
920.
Oxidation of thymine with O2 was promoted by copper(I) ion generated from reaction of L-ascorbic acid (AA) with copper (II) ion. The main oxidation products were thymine glycol (TG) and N-formyl-N'-pyruvylurea (FPU). At higher concentration of O2, formation of FPU was favored, while TG was dominant at higher Cu(II) ion and lower O2 concentrations. Reaction mechanism involving hydroxy thyminyl radical was proposed. 相似文献