全文获取类型
收费全文 | 8096篇 |
免费 | 1025篇 |
国内免费 | 200篇 |
专业分类
9321篇 |
出版年
2021年 | 102篇 |
2020年 | 74篇 |
2019年 | 82篇 |
2018年 | 98篇 |
2017年 | 103篇 |
2016年 | 171篇 |
2015年 | 207篇 |
2014年 | 245篇 |
2013年 | 314篇 |
2012年 | 415篇 |
2011年 | 442篇 |
2010年 | 279篇 |
2009年 | 230篇 |
2008年 | 327篇 |
2007年 | 349篇 |
2006年 | 330篇 |
2005年 | 301篇 |
2004年 | 292篇 |
2003年 | 281篇 |
2002年 | 314篇 |
2001年 | 215篇 |
2000年 | 203篇 |
1999年 | 192篇 |
1998年 | 97篇 |
1997年 | 104篇 |
1996年 | 86篇 |
1994年 | 88篇 |
1993年 | 78篇 |
1992年 | 171篇 |
1991年 | 125篇 |
1990年 | 149篇 |
1989年 | 126篇 |
1988年 | 121篇 |
1987年 | 139篇 |
1986年 | 135篇 |
1985年 | 139篇 |
1984年 | 122篇 |
1983年 | 101篇 |
1982年 | 84篇 |
1981年 | 82篇 |
1980年 | 82篇 |
1979年 | 99篇 |
1978年 | 115篇 |
1977年 | 77篇 |
1976年 | 84篇 |
1975年 | 76篇 |
1974年 | 92篇 |
1973年 | 89篇 |
1972年 | 74篇 |
1971年 | 72篇 |
排序方式: 共有9321条查询结果,搜索用时 0 毫秒
101.
R. J. Clarke D. Lincoln Lewis J. Alexander Williams 《BMJ (Clinical research ed.)》1972,2(5810):369-371
In a series of 68 patients with gastric ulcer who were treated by vagotomy and pyloroplasty there were no operative deaths, though one patient who received massive transfusions died 14 weeks later from hepatic necrosis probably associated with serum hepatitis. Four patients developed recurrent peptic ulceration requiring further surgical treatment. The clinical condition of all but three of the remainder was satisfactory after an average follow-up period of three years and two months. Of the 14 patients who presented with an acutely bleeding gastric ulcer, one subsequently required gastrectomy for continued bleeding; in all the others the immediate and long-term results were satisfactory. Of 21 patients with a “high” ulcer and 29 with combined gastric and duodenal ulceration one (4·8%) and three (10%) respectively suffered recurrences. We conclude that vagotomy and pyloroplasty is a satisfactory form of treatment for a high or bleeding gastric ulcer, but that for all other gastric ulcers some form of gastric resection is preferable. 相似文献
102.
Eugene D. Day Don D. Mickey Lewis C. Rigsbee Hans Meier 《Developmental neurobiology》1972,3(4):325-338
Zonal centrifuge and flotation–fractionation profile analysis of neonatal mouse brain homogenates in iso-osmotic Ficoll–sucrose density–gradients demonstrates the presence of four light density fractions. In msd neurological mutant mice with a myelin-synthesizing deficiency syndrome, the bands appear to be relatively normal until after the 10th day of postnatal brain development. With the onset of visible neurological symptoms after the 11th day, the four density bands begin to disappear from the zonal profiles and are all but absent at the time of death at about the 21st postnatal day. In normal littermates of the mutants, the bands persist with age and intensify. Although their identities remain unknown, the top three identify by their density with adult myelin and the fourth with the lighter of two adult synaptosome fractions. Mixtures of brain homogenates between mutant and normal littermates give rise to zonal and banding profiles intermediate between the separate profiles but somewhat less than their average in intensity. 相似文献
103.
The biosynthesis of collagen on polysomes has been studied by using a newly devised method for obtaining polysomes in high yield from stationary-phase mouse fibroblast (line 3T6; Goldberg &, Green, 1967). These polysomes were completely disaggregated to monosomes by brief exposure to ribonuclease and they lost most of their radioactivity to the top of the sucrose gradients as a result of a 30-minute chase with unlabeled proline. After a ten-minute pulse with [3H]proline, nascent collagen peptides could be identified in these polysomes on sucrose gradients. Most of the proline residues susceptible to hydroxylation by collagen proline hydroxylase were found, in most cases, to be already hydroxylated in these nascent peptides. The nascent nature of these peptides was confirmed by the observation that treatment of the polysomes with RNase transferred the radioactive collagen peptides to the monosome area and these peptides could subsequently be removed to the soluble material at the top of the gradient upon treatment with puromycin. These findings therefore, show clearly that the hydroxylation of proline residues is occurring, in vivo under normal conditions, on nascent collagen chains. In no case was the degree of hydroxylation of the released collagen chains higher than that on the nascent collagen peptides. It seems likely, therefore, that the major site of proline hydroxylation is the nascent collagen peptide. 相似文献
104.
Fumidil B suppressed the level of Perezia pyraustae infection in the larvae of the European corn borer, Ostrinia nubilalis, while they were feeding on diet containing the drug. After feeding ceased and the gut was emptied of diet containing Fumidil B, the level of infection again increased. Drug levels of 1000 and 1500 ppm in the meridic diet significantly reduced the mean level of P. pyraustae in the adult stage as compared with lower drug levels of 200 and 500 ppm. The level of infection increased throughout the pupal and adult stages, but during the pupal stage it increased much faster in the female than in the male. The rapid increase in the level of infection in the female is discussed in relation to transovariole transmission to the next generation. 相似文献
105.
106.
107.
D. maximum is a dominant species of outer reef flats in the Red Sea, reaching densities of about 22/m2 and biomass of 15.8 g dry tissue/m2 . A few individuals attached to loose rocks are found inside the breaker zone but they may have been dislodged by heavy seas from the outer reef flat. D. maximum feeds from a mucus net which is spread by wave action over the substratum. Hauling the net occurs at approximately 13 minute intervals throughout the 24 hours and lasts about two minutes. Neighbours with overlapping nets stimulate each other to haul and reduce feeding efficiency. The net is grasped by a pair of lateral jaws, tugged free of the substratum by rotation of the body and ingested by a zipper-like action of the lateral and marginal radula teeth. The robust, central and lateral teeth become worn, possibly while channelling out the substratum to accommodate new shell. Defaecation occurs about 2.4 times an hour, amounting to 10450 kcal/m2 /y. Females may brood simultaneously at least 11 egg capsules at various stages of development, which are suspended by stalks from the roof of the shell and pass through a dorsal slit in the mantle. Each capsule contains–500 embryos which develop into larvae with simple, coiled shells 0.33 mm in diameter. There is no planktonic phase. Adult shells amount to 2.5 kg/m2 on the outer reef flat, while dead shells are often occupied by blennies. Although D. maximum is not a specialized filter feeder, the highly developed ciliary mechanisms suggest that filtering may be an auxiliary feeding method. 相似文献
108.
A study of aldehyde dehydrogenase in rat hepatoma cells and rat hepatoma-mouse fibroblast hybrids revealed that the hepatoma cells had activity comparable to that found in whole rat liver and that the enzyme activity was suppressed in early hybrids and reappeared following chromosome loss. Starch gel electrophoresis and heat inactivation studies showed that a new form of enzyme was produced in the hybrids, possibly a heteropolymorphic combination between the HTC enzyme and a previously repressed mouse form. Staining methods for starch gel electrophoresis and histochemical detection of aldehyde dehydrogenase are described.This work was supported by grants from the Damon Runyon Foundation (DRG 1088s) and the Public Health Service (1-R01-Ca 12310-02). 相似文献
109.
110.