全文获取类型
收费全文 | 50306篇 |
免费 | 3800篇 |
国内免费 | 6174篇 |
出版年
2023年 | 857篇 |
2022年 | 1046篇 |
2021年 | 1328篇 |
2020年 | 1365篇 |
2019年 | 2045篇 |
2018年 | 1843篇 |
2017年 | 1508篇 |
2016年 | 1381篇 |
2015年 | 1322篇 |
2014年 | 2555篇 |
2013年 | 3199篇 |
2012年 | 2010篇 |
2011年 | 2429篇 |
2010年 | 1859篇 |
2009年 | 2383篇 |
2008年 | 2474篇 |
2007年 | 2701篇 |
2006年 | 2436篇 |
2005年 | 1969篇 |
2004年 | 1652篇 |
2003年 | 1648篇 |
2002年 | 1464篇 |
2001年 | 1238篇 |
2000年 | 1030篇 |
1999年 | 865篇 |
1998年 | 774篇 |
1997年 | 766篇 |
1996年 | 743篇 |
1995年 | 774篇 |
1994年 | 758篇 |
1993年 | 661篇 |
1992年 | 672篇 |
1991年 | 666篇 |
1990年 | 506篇 |
1989年 | 525篇 |
1988年 | 461篇 |
1987年 | 453篇 |
1986年 | 446篇 |
1985年 | 688篇 |
1984年 | 933篇 |
1983年 | 753篇 |
1982年 | 806篇 |
1981年 | 639篇 |
1980年 | 652篇 |
1979年 | 589篇 |
1978年 | 476篇 |
1977年 | 438篇 |
1976年 | 390篇 |
1974年 | 265篇 |
1973年 | 271篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
建立一种靶点蛋白质快速定量检测方法。在原有侧向流动免疫层析技术的基础上,通过优化层析材料和纳米微球的均一性、改进检测区的检测方法,经逐点扫描技术,建立标准浓度曲线,以达到对临床靶点蛋白质的定量检测。以乳腺癌组织中的Her2表达为例,通过对已知浓度样品的检测,验证本技术方法的准确度大于96%。另外,以蛋白质免疫印迹作为组织中特定蛋白质检测金标准,分析临床肿瘤组织中Her2蛋白的含量,其准确率也达到95.5%,而免疫组织化学方法检测准确率仅为69.58%。新型免疫层析法检测结果与靶向治疗患者的愈后密切相关(P<0.01)。改进后的新型免疫层析方法能够准确地对临床靶点蛋白质进行定量检测,而且结合侧向流动技术的简单、快速和易用性,这种新型检测方法可以广泛应用于临床组织标本、血液标本和体液标本中靶点蛋白质的临场定量检测,在一定程度上可以替代免疫组化技术。 相似文献
52.
53.
I. Siatkowski 《Biometrical journal. Biometrische Zeitschrift》1993,35(3):283-289
For some subclass of a two-way elimination of heterogeneity design, necessary and sufficient conditions are established for row-connectedness and column-connectedness of a design to imply its connectedness. 相似文献
54.
A. Bartkowiak S. sukasik K. Chwistecki 《Biometrical journal. Biometrische Zeitschrift》1991,33(6):711-718
The evaluation is based on the clinic trial with gemfibrosil (“Gevilon”, Parke-Davis) carried out in a group of 48 patients, to whom the drug was administered in the single dose of 900 mg daily during the period of 3 months. In this paper we show the results of the treatment on five biochemical Coronary Heart Disease (CHD) risk variables: Cholesterol (CHOL), High Density Lipoprotein (HDL), Triglyccrides (TGL), Uric Acid (UA) and Glucose (GL). We are concerned with a statistical model allowing to predict which and how large changes in the considered variable can be expected in a patient taking the drug. This is done considering the “regression to the mean” effect. 相似文献
55.
The explained variation in proportional hazards regression 总被引:3,自引:0,他引:3
56.
【目的】根结线虫危害严重,难防难控,前期研究发现一株深海来源的独岛枝芽胞杆菌(Virgibacillus dokdonensis) MCCC 1A00493对南方根结线虫具有良好的体外拮抗效果,本研究分离鉴定菌株发酵液中杀线虫活性物质,对其作用线虫的多种模式进行研究,为菌株有效控制植物病原线虫的应用奠定理论基础。【方法】采用硅胶柱层析和半制备高效液相色谱对独岛枝芽胞杆菌发酵上清液中的杀线虫活性物质进行分离纯化,采用液相色谱质谱联用、核磁共振对纯化物进行结构鉴定;并对其趋避、诱杀、熏杀和卵孵化抑制活性进行检测。【结果】结构鉴定确定独岛枝芽胞杆菌MCCC 1A00493发酵液中分离的杀线虫活性物质为4-乙烯基苯酚。4-乙烯基苯酚对线虫具有触杀、熏杀、卵孵化抑制和高浓度驱避低浓度引诱活性,15μg/mL 4-乙烯基苯酚72 h触杀线虫校正死亡率为71.23%±9.06%;20 mg/mL 4-乙烯基苯酚24 h熏杀线虫死亡率达100%;100μg/mL4-乙烯基苯酚作用线虫卵10d后,卵孵化抑制率达66.2%;在琼脂平板上,10mg/mL的4-乙烯基苯酚对线虫有驱避作用,1 mg/mL的4-... 相似文献
57.
在干旱、半干旱荒漠生态系统中,灌丛作为一种重要的植被类型,其独特的形态和生理适应特性能够有效促进退化生态系统结构与功能的恢复。土壤动物是荒漠生态系统中不可或缺的重要组成部分,对促进灌丛"肥岛"演变具有重要的生态作用,有利于灌丛生态功能的发挥及退化生态系统的恢复。近年来,国内外学者对荒漠灌丛微生境土壤动物的研究逐步深入,取得大量的研究成果。在此基础上,首先综述荒漠灌丛微生境土壤动物群落分布和生态功能,总结灌丛与土壤动物分布间作用关系的数学模型,针对荒漠灌丛土壤动物研究中存在的问题提出了未来可能的研究方向和建议。 相似文献
58.
59.
Dominic Moran 《Biodiversity and Conservation》1994,3(8):663-684
The financial returns to Kenyan tourism demonstrate the importance of the country's tourist potential to its economic development. Protected areas and their inhabitants are the principal focus of the tourist industry, the nations's main foreign exchange earner, and a source of wonder and value for a global population of non-users. It might be expected that such assets would be accorded some degree of security with sufficient funding to safeguard current and potential economic benefits. Yet park use is haphazard, and there is frequently little coincidence between those that benefit and those that pay for the continued existence of such areas. Growing economic and demographic pressures which threaten to swamp protected areas only emphasize the implicit subsidy currently paid by Kenyans to support conservation for the benefit of the world at large. In this climate the case for conservation depends on the measurement and capture of economic benefits. Using a contingent valuation survey of expressed preference this study estimates the consumer surplus attached to current non-consumptive use of protected areas by foreign visitors at some $450 million per annum. This sum alone is more than double the best available estimate of opportunity cost and appears to justify current resource use. The estimate is additional to current financial returns from tourism and makes no allowance for other direct and indirect benefits and potential returns from consumptive uses. Measured consumer surplus contains some margin of willingness to pay that could be captured through the current fee structure. Moreover, park fees represent the most accessible market mechanism to finance revenue sharing and additional park investment before potential recourse to emerging global market institutions. 相似文献
60.
Saldanha Bay,South Africa: recovery of Gracilaria verrucosa (Gracilariales,Rhodophyta) 总被引:2,自引:2,他引:0
Since World War II the greater Saldanha Bay lagoon system, South Africa, has been an important Gracilaria producer. Two agar factories, built in the 1960's, used Gracilaria from Saldanha Bay as their raw material. In the early 1970's the industry was destroyed as a result of dredging and marine construction operations to establish a harbor in the bay for loading ore. These environmental changes destroyed stocks and prevented the previously significant beachings of the seaweed from occurring. After a few years of no or very low commercial production, the resource slowly started to recover. The size of Gracilaria drifts increased over the following eight years to approximately one-third of the original output. This trend seems to continue. Although the stocks and resultant drifts are unlikely to recover fully to their original quantity, current production is already sufficient to ensure re-establishment of a seaweed industry in Saldanha Bay. This could have considerable socio-economic impact on the area. 相似文献