全文获取类型
收费全文 | 137237篇 |
免费 | 10245篇 |
国内免费 | 20篇 |
出版年
2023年 | 737篇 |
2022年 | 997篇 |
2021年 | 2170篇 |
2020年 | 1714篇 |
2019年 | 1969篇 |
2018年 | 3510篇 |
2017年 | 3166篇 |
2016年 | 4479篇 |
2015年 | 6152篇 |
2014年 | 6460篇 |
2013年 | 8513篇 |
2012年 | 10017篇 |
2011年 | 9351篇 |
2010年 | 6058篇 |
2009年 | 4955篇 |
2008年 | 7277篇 |
2007年 | 7057篇 |
2006年 | 6842篇 |
2005年 | 5845篇 |
2004年 | 5782篇 |
2003年 | 5213篇 |
2002年 | 4912篇 |
2001年 | 3016篇 |
2000年 | 2911篇 |
1999年 | 2419篇 |
1998年 | 1260篇 |
1997年 | 952篇 |
1996年 | 941篇 |
1995年 | 931篇 |
1994年 | 746篇 |
1993年 | 715篇 |
1992年 | 1411篇 |
1991年 | 1227篇 |
1990年 | 1145篇 |
1989年 | 1157篇 |
1988年 | 1097篇 |
1987年 | 1035篇 |
1986年 | 916篇 |
1985年 | 930篇 |
1984年 | 892篇 |
1983年 | 714篇 |
1982年 | 654篇 |
1981年 | 546篇 |
1980年 | 519篇 |
1979年 | 698篇 |
1978年 | 551篇 |
1975年 | 551篇 |
1974年 | 576篇 |
1973年 | 570篇 |
1972年 | 503篇 |
排序方式: 共有10000条查询结果,搜索用时 284 毫秒
21.
22.
23.
A newborn child was noted to have an ulcerated lesion on the vertex of her scalp, which was diagnosed as aplasia cutis congenita. As this disorder is relatively rare and frequently misdiagnosed, this case is reported and the relevant literature reviewed. 相似文献
24.
E. Molina Grima J. A. Sánchez Pérez F. García Camacho F. G. Acién Fernández J. M. Fernández Sevilla F. Valdés Sanz 《Biotechnology letters》1994,16(10):1035-1040
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. 相似文献
25.
Walking speed is a fundamental indicator for human well-being. In a clinical setting, walking speed is typically measured by means of walking tests using different protocols. However, walking speed obtained in this way is unlikely to be representative of the conditions in a free-living environment. Recently, mobile accelerometry has opened up the possibility to extract walking speed from long-time observations in free-living individuals, but the validity of these measurements needs to be determined. In this investigation, we have developed algorithms for walking speed prediction based on 3D accelerometry data (actibelt®) and created a framework using a standardized data set with gold standard annotations to facilitate the validation and comparison of these algorithms. For this purpose 17 healthy subjects operated a newly developed mobile gold standard while walking/running on an indoor track. Subsequently, the validity of 12 candidate algorithms for walking speed prediction ranging from well-known simple approaches like combining step length with frequency to more sophisticated algorithms such as linear and non-linear models was assessed using statistical measures. As a result, a novel algorithm employing support vector regression was found to perform best with a concordance correlation coefficient of 0.93 (95%CI 0.92–0.94) and a coverage probability CP1 of 0.46 (95%CI 0.12–0.70) for a deviation of 0.1 m/s (CP2 0.78, CP3 0.94) when compared to the mobile gold standard while walking indoors. A smaller outdoor experiment confirmed those results with even better coverage probability. We conclude that walking speed thus obtained has the potential to help establish walking speed in free-living environments as a patient-oriented outcome measure. 相似文献
26.
Twenty four male Wistar rats weighing 250 +/- 10 g, in three groups of 8 rats each, were used. Group A was used as control and the content of its drinking water was 6.5 mg/l Ca; 2.4 mg/l Mg. The drinking water of groups B and C was supplemented with 20 mM (SrCl2) and 20 mM (MgCl2), respectively. Once the 20 days of mineral supplementation had passed, arterial blood was extracted by puncture in the abdominal aorta. In the serum obtained after centrifugation, Ca, Mg, Sr and the total proteins (TP) were determined. Afterwards the serum was subjected to ultrafiltration. Concentrations of Ca, Mg and TP were measured in the obtained ultrafiltrates (u), with the above described techniques. The pH was measured before and after the ultrafiltration. The TP decreased significantly both in group B (supplemented with Sr), and in group C (supplement with Mg). Increases in Ca were found in group B and in Mg in group C. The Mg/Ca ratio increased 10% after the supplementation with Mg. At the ultrafiltrate a significant increase in Cau after supplementation with Sr and with Mg was observed. The Mgu/Cau ratio decreased 14% in the group supplemented with Sr and 38% after the supplementation with Mg. In conclusion, the supplementation with Sr (20 mM) in rats increases the Cau and could have the effect of reducing protein synthesis. These facts should be borne in mind when Sr is used for therapeutical purposes. 相似文献
27.
The existence of duodeno-gastric reflux was evaluated in a group of 15 healthy subjects, in fasting and for 24 hours. The assessment of duodeno-gastric reflux was made by quantitation of the bile acids (BA) present in the gastric juice. The individual free and conjugated BA were separated and quantified by means of thin-layer chromatography and in situ spectrofluorometry. In 7 of the subjects studied no BA were detected, and in the other 8 subjects the BA levels were below 6 mumol reflux/hour. There were no free BA detected in any of the subjects. The levels of BA in gastric juice increased progressively with age, but there were no differences between sex. The chromatographic technique used is highly sensitive for the analysis of BA in biological samples. The study of BA in the gastric juice provides a quantitative and reliable assessment of the degree of duodeno-gastric reflux. 相似文献
28.
29.
Carmen de Sena-Tomás Mónica Navarro-González Ursula Kües José Pérez-Martín 《Genetics》2013,195(1):47-57
The fungal fruiting body or mushroom is a multicellular structure essential for sexual reproduction. It is composed of dikaryotic cells that contain one haploid nucleus from each mating partner sharing the same cytoplasm without undergoing nuclear fusion. In the mushroom, the pileus bears the hymenium, a layer of cells that includes the specialized basidia in which nuclear fusion, meiosis, and sporulation occur. Coprinopsis cinerea is a well-known model fungus used to study developmental processes associated with the formation of the fruiting body. Here we describe that knocking down the expression of Atr1 and Chk1, two kinases shown to be involved in the response to DNA damage in a number of eukaryotic organisms, dramatically impairs the ability to develop fruiting bodies in C. cinerea, as well as other developmental decisions such as sclerotia formation. These developmental defects correlated with the impairment in silenced strains to sustain an appropriated dikaryotic cell cycle. Dikaryotic cells in which chk1 or atr1 genes were silenced displayed a higher level of asynchronous mitosis and as a consequence aberrant cells carrying an unbalanced dose of nuclei. Since fruiting body initiation is dependent on the balanced mating-type regulator doses present in the dikaryon, we believe that the observed developmental defects were a consequence of the impaired cell cycle in the dikaryon. Our results suggest a connection between the DNA damage response cascade, cell cycle regulation, and developmental processes in this fungus. 相似文献