全文获取类型
收费全文 | 587篇 |
免费 | 35篇 |
专业分类
622篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 20篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 31篇 |
2014年 | 37篇 |
2013年 | 38篇 |
2012年 | 55篇 |
2011年 | 42篇 |
2010年 | 28篇 |
2009年 | 18篇 |
2008年 | 26篇 |
2007年 | 40篇 |
2006年 | 29篇 |
2005年 | 32篇 |
2004年 | 30篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有622条查询结果,搜索用时 15 毫秒
611.
Patricio López-Jaramillo Lina P Pradilla Vicente Lahera Federico A Silva Sieger Christian F Rueda-Clausen Gustavo A Márquez 《Trials》2006,7(1):1-12
In ageing men testosterone levels decline, while cognitive function, muscle and bone mass, sexual hair growth, libido and sexual activity decline and the risk of cardiovascular diseases increase. We set up a double-blind, randomized placebo-controlled trial to investigate the effects of testosterone supplementation on functional mobility, quality of life, body composition, cognitive function, vascular function and risk factors, and bone mineral density in older hypogonadal men. We recruited 237 men with serum testosterone levels below 13.7 nmol/L and ages 60–80 years. They were randomized to either four capsules of 40 mg testosterone undecanoate (TU) or placebo daily for 26 weeks. Primary endpoints are functional mobility and quality of life. Secondary endpoints are body composition, cognitive function, aortic stiffness and cardiovascular risk factors and bone mineral density. Effects on prostate, liver and hematological parameters will be studied with respect to safety. Measure of effect will be the difference in change from baseline visit to final visit between TU and placebo. We will study whether the effect of TU differs across subgroups of baseline waist girth (< 100 cm vs. ≥ 100 cm; testosterone level (<12 versus ≥ 12 nmol/L), age (< median versus ≥ median), and level of outcome under study (< median versus ≥ median). At baseline, mean age, BMI and testosterone levels were 67 years, 27 kg/m2 and 10.72 nmol/L, respectively. 相似文献
612.
613.
614.
Patricio Hernáez Amanda M. Windsor Caio Augusto Paula William Santana 《Marine Biology Research》2020,16(1):50-60
ABSTRACTA new species of ghost shrimp, Neocallichirus pinheiroi, is described based on specimens collected in subtidal habitats of Saquaira beach, northeastern coast of Brazil. This new species resembles N. lemaitrei Manning, 1993, but differs from it primarily in having a third maxilliped propodus expanded ventrally, and in the case of males, a large subtriangular tooth on the cutting edge of the major cheliped dactylus. Diagnostic features of the new species include: (i) frontal margin of carapace with rounded lateral projections not exceeding rostrum distal margin, (ii) third maxilliped carpus with row of sclerotized setae on median internal surface, (iii) minor cheliped with cutting edge of dactylus microscopically pectinate, (iv) endopod of male second pleopod with appendices interna and masculina. This is the seventh described species of the genus Neocallichirus from the western Atlantic and the fourth report of this genus in Brazil. A key for identification of western Atlantic species belonging to the genus is provided. 相似文献
615.
616.
B B Fuks A I Shapoval I Grzhebin IM 《Biulleten' eksperimental'no? biologii i meditsiny》1991,112(7):78-80
We investigated the phenomenon of increased sensitivity of tumor-bearing mice to endotoxin shock. I/V administration of sera from tumor (EL-4, B16, R815, MOPC-315) bearers or tumoral culture media into intact mice caused the increased sensitivity to lethal action of LPS plus GMDP. Production of TNF in above mice was also significantly increased under the influence of LPS plus GMDP. Sensitivity induced factors in tumor bearing mice sera have mol. weight more than 50 kDa. This action was partially abolished by indomethacin. 相似文献
617.
Nicholas L. Cross Patricio Morales Masaru Fukuda Esmail Behboodi 《American journal of primatology》1989,17(2):157-163
The acrosome of Macaca fascicularis sperm cannot be distinguished by conventional light microscopy, so determining whether sperm are acrosome-intact or-reacted is difficult. We describe methods for labeling the acrosomal region of sperm with two different probes: fluoresceinated Pisum sativum agglutinin and anti-sperm antiserum. Acrosome-intact sperm are much more heavily labeled in the acrosomal region than are acrosome-reacted sperm, providing a simple means of differentiating the two types of sperm. The two probes detect similar numbers of acrosome-reacted sperm following treatment with the divalent cation ionophore, A23187. 相似文献
618.
Rolando C. Rossi Segio B. Kaufman Rodolfo M. Gonzlez Lebrero Jens G. Nrby Patricio J. Garrahan 《Analytical biochemistry》1999,270(2):276-285
The present paper describes a quenching-and-washing chamber (QWC) to be used with a rapid-mixing apparatus (RMA) for the study of processes in the millisecond time scale. The QWC enables fast, nondestructive quenching by cooling and dilution of reactants in particulate systems that can be trapped on a filter. The reaction mixture (e.g., at 25 degrees C) is injected from the RMA into the QWC where it is immediately mixed with a stream of ice-cold solution flowing at a rate of 15-40 ml s-1. Quenching requires that the process studied is slowed considerably by cooling to 0-2 degrees C and/or by removal of reactants by dilution. The equipment was characterized through a study of the tight binding (occlusion) of 86Rb+ to purified, membrane-bound Na+/K+-ATPase. Millipore filters of 0.22-0.80 microm pore size trapped close to 100% of the enzyme protein. Enzyme with occluded 86Rb+ was formed in the RMA under conditions where the rate constant for release of Rb+ at 25 degrees C is up to 25 s-1 and then injected into the QWC. The high off-rate constant is due to the presence of 2.5 mM ATP, which accelerates release of Rb+. The recovery of occluded 86Rb+ on the filter was at least 90%, indicating that both cooling of the reactants and dilution of ATP are fast enough to stop the reaction. The quenching time was 3-4 ms. 相似文献
619.
Cecilia Smith-Ramírez Iván Díaz Patricio Pliscoff Claudio Valdovinos Marco A. Méndez Juan Larraín Horacio Samaniego 《Biodiversity and Conservation》2007,16(9):2627-2648
Knowledge of species richness centers is necessary for the design of conservation areas. In this study, we present a GIS analysis
of two years of field data on animal and plant diversity distributions in evergreen, coastal rain forests of southern Chile
(39°30′–41°25′ S). Despite their high endemism, these forests have remained largely unprotected. Field records were complemented
with data from museum collections and scientific literature. We used selected environmental variables (evapotranspiration,
altitude) and, in some cases, forest types as predictors of species distributions. Our study focused on the distribution of
forest bryophytes, vascular plants, soil invertebrates, amphibians and birds. We generated distributional maps for each taxa
based on their field records in the study area, complemented by natural history information, except in the case of bryophytes
and soil invertebrates. In general, species richness was lower at 600 m elevation or above for all the taxa studied. Species
richness tends to increase in the northern sector of the study area. We observed a greater richness of vascular plants near
rivers and streams, and noted important floristic differences between west and east-facing slopes of the Coastal Range, with
more species in the oriental side. Because species in high altitude forests are not a subset of those found at lower elevations,
we propose that conservation strategies should prioritize the protection of the entire altitudinal gradient of the southern
Coastal Range, especially in the more diverse oriental and northern sectors. 相似文献
620.
We detected that Galaxias maculatus exhibits a pattern where metabolic activity increases after sunrise and peaks between noon and sunset, but this species feeds in the afternoon, until several hours after sunset. Moreover, we showed that G. maculatus is observed in the littoral zone during the day, disappears completely from this zone after sunset and returns at sunrise. Littoral prey species are common in the diet of G. maculatus, but this study showed that pelagic prey is also present during twilight and night hours in smaller individuals (<50 mm), which is related to habitat use. These behavioural rhythms are especially important for G. maculatus, which runs a high predation risk when consuming prey that is widely available outside the littoral zone. This risk is ameliorated under the protection of low light intensity. Thus, G. maculatus is a key species linking lower trophic levels, such as the plankton community, to higher levels of native and exotic piscivores. These displacements of G. maculatus generate an active flow of energy and matter between habitats, with a potentially profound effect on the entire food network and energy dynamics of the lake. 相似文献