全文获取类型
收费全文 | 6540篇 |
免费 | 281篇 |
国内免费 | 695篇 |
专业分类
7516篇 |
出版年
2023年 | 79篇 |
2022年 | 127篇 |
2021年 | 165篇 |
2020年 | 138篇 |
2019年 | 271篇 |
2018年 | 337篇 |
2017年 | 226篇 |
2016年 | 142篇 |
2015年 | 176篇 |
2014年 | 337篇 |
2013年 | 448篇 |
2012年 | 270篇 |
2011年 | 231篇 |
2010年 | 186篇 |
2009年 | 229篇 |
2008年 | 244篇 |
2007年 | 226篇 |
2006年 | 154篇 |
2005年 | 164篇 |
2004年 | 179篇 |
2003年 | 120篇 |
2002年 | 178篇 |
2001年 | 147篇 |
2000年 | 163篇 |
1999年 | 128篇 |
1998年 | 115篇 |
1997年 | 101篇 |
1996年 | 90篇 |
1995年 | 83篇 |
1994年 | 97篇 |
1993年 | 102篇 |
1992年 | 88篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1987年 | 42篇 |
1985年 | 100篇 |
1984年 | 177篇 |
1983年 | 177篇 |
1982年 | 188篇 |
1981年 | 140篇 |
1980年 | 116篇 |
1979年 | 119篇 |
1978年 | 96篇 |
1977年 | 120篇 |
1976年 | 83篇 |
1975年 | 77篇 |
1974年 | 49篇 |
1973年 | 41篇 |
排序方式: 共有7516条查询结果,搜索用时 0 毫秒
151.
Mass treatment with ivermectin for filariasis control in Papua New Guinea: impact on mosquito survival 总被引:1,自引:0,他引:1
M. J. Bockarie J. L. K. Hii N. D. E. Alexander F. Bockarie H. Dagoro J. W. Kazura M. P. Alpers 《Medical and veterinary entomology》1999,13(2):120-123
Field studies were carried out to determine the impact of mass human treatment with ivermectin on the survival of anthropophagic mosquitoes of the Anopheles punctulatus complex (Diptera: Culicidae), the vectors of lymphatic filariasis and malaria in Papua New Guinea. In a village where mass treatment had been given, using 400 microg/kg ivermectin plus 6 mg/kg diethylcarbamazine citrate (DEC), we performed pre- and post-treatment collections of freshly blood-engorged mosquitoes from the same nine bedrooms. All blood-fed mosquitoes collected less than 4 days after mass treatment died within 9 days, whereas 67% of those collected before treatment survived for >9 days. Comparison (using the log-rank test) of the survival curves for mosquitoes collected (i) before treatment, (ii)<4 days after treatment, and (iii) 28 days after treatment, showed the survival rate of group (ii) to be significantly lower than the other two (chi2=176, df=2, P<0.0001). Pre- and post-treatment all-night landing catches showed no reduction in human biting rates in the experimental village. In another village, where people were mass treated with ivermectin (400 microg/kg) only, the survival rates of freshly blood-engorged An. punctulatus collected from bedroom resting-sites less than 1 day after treatment, were compared to similar collections carried out at the same time in a nearby village where people were not treated with ivermectin. The 48-h survival rate for the ivermectin-treated village was 31% compared to 94% for the other; this difference was highly significant (chi2=32.42, df=1, P<0.0001). Mosquitoes fed 2 months post-treatment with DEC or collected 38 days post-treatment with ivermectin had normal survival rates. We conclude that the duration of the systemic lethal effect of ivermectin on mosquitoes is insufficient to be of epidemiological significance in filariasis control programmes that are based on biannual and annual single-dose treatments, but might reduce vectorial capacity sufficiently to block epidemics of dengue or even malaria. 相似文献
152.
Genome-wide methylation studies frequently lack adequate controls to estimate proportions of background reads in the resulting datasets. To generate appropriate control pools, we developed technique termed nMETR (non-methylated tag recovery) based on digestion of genomic DNA with methylation-sensitive restriction enzyme, ligation of adapter oligonucleotide and PCR amplification of non-methylated sites associated with genomic repetitive elements. The protocol takes only two working days to generate amplicons for deep sequencing. We applied nMETR for human DNA using BspFNI enzyme and retrotransposon Alu-specific primers. 454-sequencing enabled identification of 1113 nMETR tag sites, of them ~65% were parts of CpG islands. Representation of reads inversely correlated with methylation levels, thus confirming nMETR fidelity. We created software that eliminates background reads and enables to map and annotate individual tags on human genome. nMETR tags may serve as the controls for large-scale epigenetic studies and for identifying unmethylated transposable elements located close to genomic CpG islands. 相似文献
153.
Glucose metabolism and insulin secretion were studied in isolated rat pancreatic islets of different sizes and the amount of tissue was quantitated by the measurement of DNA. It was found that larger islets (140-210 ng DNA/islet) utilized more glucose (based on the conversion of 3H-5-glucose to [3H]20) per ng of DNA than islets containing less DNA (60-120 ng/islet). However, the insulin secreted per ng of DNA in response to a given glucose concentration was the same in islets of all sizes. Also, the islet insulin and glucagon content when expressed in terms of DNA did not depend upon islet size. Thus, although glucose utilization rates expressed as a function of islet DNA content were greater in larger islets, no such relationship was found for glucose-induced insulin release or insulin and glucagon content. 相似文献
154.
J E Morley T Yamada J H Walsh C B Lamers H Wong A Shulkes D A Damassa J Gordon H E Carlson J M Hershman 《Life sciences》1980,26(26):2239-2244
This study demonstrates that, during morphine addiction and withdrawal in rats profound alterations in the concentrations of a variety of brain peptides occur. Somatostatin, cholecystokinin, neurotensin and substance P concentrations increased during morphine addiction. Naloxone-induced withdrawal decreased brain concentrations of TRH, somatostatin, neurotensin and substance P. Naloxone alone decreased thalamic substance P and neurotensin concentrations. Vasoactive intestinal peptide concentrations were unaltered by any of the treatments. The fall in the tissue concentration of somatostatin during naloxone-induced withdrawal correlated well with the fall in the circulating growth hormone, suggesting that this could be secondary to somatostatin release. Our data support the hypothesis that brain peptides, acting locally in the brain as neuromodulators, play an important role in the genesis of the syndromes of morphine addiction and withdrawal. 相似文献
155.
In perfused rat liver, the effects of various hormones on the stimulation of phosphorylation and allosteric properties of purified phosphorfructokinase were investigated. Rat livers were perfused with [32P]phosphate followed with various hormones or cyclicAMP, and 32P-labeled phosphofructokinase was isolated. 32P incorporation into the enzyme and enzyme inhibition by ATP or citrate were determined. Only glucagon increased the 32P incorporation into phosphofructokinase and this increase was approximately threefold. The cyclicAMP level was increased simultaneously approximately four- to fivefold compared to the control perfused liver. Similar results were obtained by perfusing the liver with cyclicAMP (0.1 mm). The phosphorylated phosphofructokinase showed a decrease in the Ki values for ATP (from 0.4 to 0.2 mm) and citrate (from 2 to 0.6 mm). Neither epinephrine nor insulin affected the extent of phosphorylation or the allosteric properties of the enzyme. The half-maximal concentration of glucagon required for phosphorylation of phosphofructokinase and modification of its allosteric properties was approximately 6 × 10?11m. It is concluded that glucagon increases the inhibition of liver phosphofructokinase by ATP and citrate through phosphorylation of the enzyme involving a β-receptor-mediated cyclicAMP-dependent mechanism. 相似文献
156.
Enrique Peñalver 《法国昆虫学会纪事》2013,49(1-2):138-147
During a palaeontological excavation of amber at the site named San Just, in the Utrillas-Escucha area of Teruel Province, northeastern Spain, a rich fauna from the Albian (Early Cretaceous) was discovered. Among it, three specimens of Thysanoptera were found that are here attributed to the new genus Hispanothrips n. gen. in the family Stenurothripidae Bagnall 1923. Phylogenetic analyses were conducted that support the resurrection of the family Stenurothripidae and its replacement for Adiheterothripidae Shumsher 1946. 相似文献
157.
Peter S. Cranston 《水生昆虫》2013,35(2):103-114
A new dipteran species, Parapsectra wagneri sp. n. (Chironomidae), is described from emergence traps on Breitenbach, Schlitz, Germany. It differs in antennal ratio and characteristics of the genitalia from the three known species. 相似文献
158.
目的 探讨住院患者多重耐药菌感染情况与病原学特点,为临床制定医院感染控制措施提供参考依据.方法 对住院患者中的多重耐药菌感染及病原特点情况进行统计分析.结果 住院患者多重耐药菌感染发生率为3.5%,主要为革兰阴性菌(71.5%),多重耐药菌居前7位的依次是大肠埃希菌、肺炎克雷伯菌、鲍曼不动杆菌、铜绿假单胞菌、凝固酶阴性葡萄球菌、肠球菌属、金黄色葡萄球菌等.多重耐药菌感染的患者主要来自于重症监护室、神经外科、呼吸内科等.多重耐药菌对选用的抗生素均有较高的耐药性.结论 多重耐药菌耐药率普遍较高,临床医师应重视病原学检查及药敏监测,合理选择使用抗菌药物. 相似文献
159.
160.
本文报道了寄生在水稻子房上的绿核菌属一新种,稻白色绿枝菌Ustilaginoideaalbicansspnov。该菌的侵染时期、发病时期和症状与稻曲病毒U,virens相似,但该新种产生白色分生泡子座。分生孢子球形或椭球形,表面光滑,白色,无疣突,35~60X35~6.8μm。未见菌核。以分离的稻白色绿核菌回接水稻,可以产生同样的白色稻曲球。模式标本和模式菌株保存在辽宁省农业科学院植保所。 相似文献