全文获取类型
收费全文 | 89036篇 |
免费 | 6110篇 |
国内免费 | 16篇 |
专业分类
95162篇 |
出版年
2023年 | 579篇 |
2022年 | 757篇 |
2021年 | 1468篇 |
2020年 | 1200篇 |
2019年 | 1379篇 |
2018年 | 2511篇 |
2017年 | 2303篇 |
2016年 | 3031篇 |
2015年 | 4000篇 |
2014年 | 4184篇 |
2013年 | 5525篇 |
2012年 | 6510篇 |
2011年 | 5991篇 |
2010年 | 3876篇 |
2009年 | 3271篇 |
2008年 | 4788篇 |
2007年 | 4590篇 |
2006年 | 4236篇 |
2005年 | 3640篇 |
2004年 | 3611篇 |
2003年 | 3243篇 |
2002年 | 2982篇 |
2001年 | 2123篇 |
2000年 | 2077篇 |
1999年 | 1657篇 |
1998年 | 844篇 |
1997年 | 630篇 |
1996年 | 624篇 |
1995年 | 587篇 |
1994年 | 491篇 |
1993年 | 465篇 |
1992年 | 888篇 |
1991年 | 804篇 |
1990年 | 738篇 |
1989年 | 715篇 |
1988年 | 665篇 |
1987年 | 629篇 |
1986年 | 571篇 |
1985年 | 563篇 |
1984年 | 512篇 |
1983年 | 408篇 |
1982年 | 353篇 |
1981年 | 273篇 |
1980年 | 274篇 |
1979年 | 362篇 |
1978年 | 326篇 |
1975年 | 315篇 |
1974年 | 352篇 |
1973年 | 354篇 |
1972年 | 299篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
A Soler C García del Río L García-Torres F Vargas A Martín-Andrés C Osorio 《Revista Espanola de Fisiología》1985,41(1):107-116
The effects of changes in arterial pressure and in circulating volume on Plasma Renin Activity (PRA) in the intact rat were compared by two experimental procedures. Gradual volume depletion was induced by intraperitoneal injection of a hyperoncotic polyethyleneglycol solution (PEG) in absence of acute changes in Systolic Arterial Pressure (SAP). SAP was measured in the conscious state by the tail cuff technique. Plasma Protein Concentration (PPC) and Hematocrit (Hct) increases after PEG injection were compared as the index for measuring the Plasma Volume Reduction (PVR). PRA showed a significant (p less than 0.001) linear relationship with PPC, suggesting a direct dependence of renin secretion on volume depletion. Acute changes in the circulating volume were induced by controlled hemorrhages of 5.0, 10.0, 15.0 and 20.0 ml of blood/kg body weight. The increase in PRA showed a significant relationship with the changes in circulating volume, but it did not show any dependence on the changes in Mean Arterial Pressure (MAP). Our results suggest that, in the intact and conscious rat, renin secretion responds to the information from the cardiopulmonary volume receptors rather than to that from the high pressure receptors. 相似文献
92.
93.
94.
Hana Votavová Vladimír Gut Karel Bláha Jaroslav Šponar 《International journal of biological macromolecules》1982,4(6):341-346
DNA complexes with polypeptides (Lys-Ala-Ala)1)] and (Lys-Ala-Ala)34 have been studied using the methods of thermal melting and circular dichroism. Derivative melting curves of (Lys-Ala-Ala)10 DNA differed substantially from those of (Lys-Ala-Ala)34 prepared either by salt gradient dialysis or by direct mixing. Melting curves of the former complex were unimodal or bimodal with Tm increasing continuously withn input lysin-to-DNA phosphate ratio (r); those of the latter complex consisted of three separate transitions with Tm values almost independent of r. Complete reversibility of binding in the (Lys-Ala-Ala)10-DNA system but a slow redistribution of (Lys-Ala-Ala)34 on DNA at low temperature were found in the redistribution experiments Much faster redistribution from denatured to native DNA occurs at the temperature of melting, contributing to the unusual trimodal melting pattern. Circular dichroism curves are very similar for both complexes and indicate little change of DNA conformation upon polypeptide binding. 相似文献
95.
Susanne Berglund Bryan J. Egner Henrik Gradén Joakim Gradén David G.A. Morgan Tord Inghardt Fabrizio Giordanetto 《Bioorganic & medicinal chemistry letters》2009,19(15):4268-4273
Herein, we disclose the discovery and optimization of 2-piperidin-4-yl-acetamide derivatives as MCH-R1 antagonists. Structural investigation of piperidin-4-yl-amide and piperidin-4-yl-ureas identified 2-piperidin-4-yl-acetamide-based MCH-R1 antagonists with outstanding in vivo efficacy but flawed with high affinity towards the hERG potassium channel. While existing hERG SAR information was employed to discover highly potent MCH-R1 antagonists with minimized hERG inhibition, additional hurdles prevented their subsequent clinical exploration. 相似文献
96.
97.
E. L. García Diez J. L. Labajo Salazar F. de Pablo Dávila 《International journal of biometeorology》1993,37(4):194-199
The present paper offers data on the effect of certain meteorological parameters on the outbreak of forest fires in Galicia (Spain). In a day-to-day analysis, the values of the stability of the air column and the saturation deficit at the lower levels are related to the number of fires occurring in the following 24 h. 相似文献
98.
F Rabanal I Haro F Reig J M García-Antón 《International journal of peptide and protein research》1990,36(1):26-30
The synthesis of three hepatitis B surface antigens derived from S and pre-S proteins (adw S(140-147), [Tyr148] adw S(139-148), and adw pre-S(120-145)) has been accomplished by the continuous flow Fmoc-polyamide solid phase method. The use of different scavengers and trimethylsilyl bromide (TMSBr) in trifluoroacetic acid as deprotecting procedures is discussed. 相似文献
99.
A frameshift mutation (2869insG) in the second transmembrane domain of the CFTR gene: identification, regional distribution, and clinical presentation. 下载免费PDF全文
100.
Development of the visual system of anchovy larvae,Engraulis anchoita: A microanatomical description
Valeria Miranda Stefanía Cohen Alcira O. Díaz Marina V. Diaz 《Journal of morphology》2020,281(4-5):465-475
During the early ontogeny of fish larvae, the accurate development of the visual system plays a key role, because it is involved in locating food, orientation, selection of favorable habitat, and evasion of predators. The structure of the eye of the fish is typical of vertebrates, with some modifications related to the aquatic environment. In the present work, we describe the development of the larval eye of Engraulis anchoita for the first time. Larvae were collected at the Permanent Station of Environmental Studies (EPEA) in coastal waters of the Southwestern Atlantic Ocean during research cruises in 2015 and 2016. We describe the histology of the retina layers, determine the beginning of the functionality of the eye, and discuss a possible synchronization with the development of the digestive tract. This study provides information about the biology of E. anchoita, the most abundant fish species in the southwestern Atlantic Ocean. Also, recent studies have shown responses of the retina and other tissues to the increase in environmental acidity. Therefore, results of this study are also discussed with respect to the possible effect of acidification on the larvae of this species. The continuity of the time series developed at the EPEA will allow monitoring the effect of long-term environmental and biological variables on the early ontogeny of anchovy in the context of climate change. The high commercial fishing potential of E. anchoita due to its high abundance, as well as its essential role in the trophic web of other commercially valuable fishing resources of Argentina, reinforce the need to continue deepening knowledge about this species. Research highlights:
- Eyes of Engraulis anchoita larvae are functional from early larval stages.
- At hatching, the retina is formed by only few layers from which the other layers differentiates during ontogeny.
- Focal distance increases with larval growth.