全文获取类型
收费全文 | 11159篇 |
免费 | 870篇 |
国内免费 | 6篇 |
专业分类
12035篇 |
出版年
2023年 | 75篇 |
2022年 | 191篇 |
2021年 | 287篇 |
2020年 | 158篇 |
2019年 | 285篇 |
2018年 | 315篇 |
2017年 | 280篇 |
2016年 | 411篇 |
2015年 | 633篇 |
2014年 | 641篇 |
2013年 | 848篇 |
2012年 | 971篇 |
2011年 | 912篇 |
2010年 | 571篇 |
2009年 | 546篇 |
2008年 | 669篇 |
2007年 | 684篇 |
2006年 | 577篇 |
2005年 | 519篇 |
2004年 | 457篇 |
2003年 | 416篇 |
2002年 | 382篇 |
2001年 | 99篇 |
2000年 | 65篇 |
1999年 | 83篇 |
1998年 | 97篇 |
1997年 | 67篇 |
1996年 | 64篇 |
1995年 | 67篇 |
1994年 | 64篇 |
1993年 | 42篇 |
1992年 | 57篇 |
1991年 | 44篇 |
1990年 | 28篇 |
1989年 | 42篇 |
1988年 | 25篇 |
1987年 | 27篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 28篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 21篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1974年 | 18篇 |
1972年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Carlo Alviggi Alberto Revelli Paola Anserini Antonio Ranieri Luigi Fedele Ida Strina Marco Massobrio Nicola Ragni Giuseppe De Placido 《Reproductive biology and endocrinology : RB&E》2007,5(1):45-7
Background
Multifollicular ovarian stimulation (MOS) is widely used in IVF and the compliance to treatment is deeply influenced by the tolerability of the medication(s) used and by the ease of self-administration. This prospective, controlled, randomised, parallel group open label, multicenter, phase III, equivalence study has been aimed to compare the clinical effectiveness (in terms of oocytes obtained) and tolerability of subcutaneous (s.c.) self-administered versus classical intramuscular (i.m.) injections of Merional, a new highly-purified hMG preparation. 相似文献902.
Background
It is generally assumed that primordial cells had small genomes with simple genes coding for enzymes able to react with a wide range of chemically related substrates, interconnecting different metabolic routes. New genes coding for enzymes with a narrowed substrate specificity arose by paralogous duplication(s) of ancestral ones and evolutionary divergence. In this way new metabolic pathways were built up by primordial cells. Useful hints to disclose the origin and evolution of ancestral metabolic routes and their interconnections can be obtained by comparing sequences of enzymes involved in the same or different metabolic routes. From this viewpoint, the lysine, arginine, and leucine biosynthetic routes represent very interesting study-models. Some of the lys, arg and leu genes are paralogs; this led to the suggestion that their ancestor genes might interconnect the three pathways. The aim of this work was to trace the evolutionary pathway leading to the appearance of the extant biosynthetic routes and to try to disclose the interrelationships existing between them and other pathways in the early stages of cellular evolution.Results
The comparative analysis of the genes involved in the biosynthesis of lysine, leucine, and arginine, their phylogenetic distribution and analysis revealed that the extant metabolic "grids" and their interrelationships might be the outcome of a cascade of duplication of ancestral genes that, according to the patchwork hypothesis, coded for unspecific enzymes able to react with a wide range of substrates. These genes belonged to a single common pathway in which the three biosynthetic routes were highly interconnected between them and also to methionine, threonine, and cell wall biosynthesis. A possible evolutionary model leading to the extant metabolic scenarios was also depicted.Conclusion
The whole body of data obtained in this work suggests that primordial cells synthesized leucine, lysine, and arginine through a single common metabolic pathway, whose genes underwent a set of duplication events, most of which can have predated the appearance of the last common universal ancestor of the three cell domains (Archaea, Bacteria, and Eucaryotes). The model proposes a relative timing for the appearance of the three routes and also suggests a possible evolutionary pathway for the assembly of bacterial cell-wall.903.
904.
Background
The alterations in skeletal muscle structure and function after prolonged periods of unloading are initiated by the chronic lack of mechanical stimulus of sufficient intensity, which is the result of a series of biochemical and metabolic interactions spanning from cellular to tissue/organ level. Reduced activation of skeletal muscle alters the gene expression of myosin heavy chain isoforms to meet the functional demands of reduced mechanical load, which results in muscle atrophy and reduced capacity to process fatty acids. In contrast, chronic loading results in the opposite pattern of adaptations. 相似文献905.
Flores-Ramírez LA Liñán-Cabello MA 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2007,146(1-2):194-202
To examine the response to exposure to a thermal gradient in coral, we assessed the effect of a gradual 10 degrees C temperature increase (22 to 32 degrees C over 10 h) on normal (N), partially bleached (P) and control (C) samples collected from different branches of the same coral (Pocillopora capitata). We examined markers of oxidative stress, including lipid peroxidation (MDA) and superoxide dismutase (SOD) activity, indicators of bleaching, including chlorophyll a (Chl a) and carotenoid pigment (PC) levels, as well as zooxanthellae density. Our results revealed that N, P and C coral samples all contained higher levels of PC versus Chl a. The levels of both pigments increased as the temperature increased from 22 to 28 degrees C only in N and C samples, whereas P samples showed less cellular damage than N and C samples at temperatures between 26 and 28 degrees C, and had greater antioxidant activities at temperatures between 26 and 30 degrees C. The rate of zooxanthellar expulsion consistently increased with temperature in all three coral types across the entire temperature range. Collectively, these results indicate that temperature has a direct effect on the antagonistic relationship between temperature-induced damage and protective antioxidant mechanisms in this type of coral. 相似文献
906.
907.
Cifoni Marco Boggero Angela Rogora Michela Ciampittiello Marzia Martnez Alejandro Galassi Diana Maria Paola Fiasca Barbara Di Lorenzo Tiziana 《Hydrobiologia》2022,849(16):3545-3564
Hydrobiologia - Human-induced water level fluctuations (WLFs) are among the major pressures threatening lake ecosystems. Their effect on meiobenthic species of the littoral zone has been... 相似文献
908.
Alesci Marco Smith Rebecca L. Ayala Santacruz Jorge Damian Camperio Ciani Andrea 《Primates; journal of primatology》2022,63(2):161-171
Primates - Increasing urbanisation is encroaching into natural habitats and sometimes forcing wildlife into urban centres. Whether or not wildlife can thrive in an urban environment is dependent on... 相似文献
909.
Randrianarison Rose Marie Lutz Meredith Torti Valeria Tan Chia Bonadonna Giovanna Randrianambinina Blanchard Rasoloharijaona Solofonirina Rabarison Harison Miaretsoa Longondraza Rarojoson Nianja Jemisa De Gregorio Chiara Valente Daria Gamba Marco Ratsimbazafy Jonah Giacoma Cristina 《International journal of primatology》2022,43(4):584-610
International Journal of Primatology - Deforestation around the world is a major threat to primates. Understanding primate species’ habitat and dietary requirements is critical in creating... 相似文献
910.
Schunck Fabio Rodrigues Kleber Evangelista da Silva Marco Aurélio Galvão Prates Cristine Albano Ciro Piacentini Vítor Q. 《Acta ethologica》2022,25(3):135-140
acta ethologica - The Brazilian ruby, Heliodoxa rubricauda, is a forest species of hummingbird endemic to the Atlantic Forest. It belongs to an Andean clade of birds with robust and strong legs and... 相似文献