全文获取类型
收费全文 | 12235篇 |
免费 | 1170篇 |
国内免费 | 3篇 |
专业分类
13408篇 |
出版年
2023年 | 51篇 |
2022年 | 128篇 |
2021年 | 261篇 |
2020年 | 147篇 |
2019年 | 185篇 |
2018年 | 230篇 |
2017年 | 200篇 |
2016年 | 351篇 |
2015年 | 575篇 |
2014年 | 603篇 |
2013年 | 692篇 |
2012年 | 936篇 |
2011年 | 887篇 |
2010年 | 562篇 |
2009年 | 508篇 |
2008年 | 720篇 |
2007年 | 711篇 |
2006年 | 678篇 |
2005年 | 667篇 |
2004年 | 626篇 |
2003年 | 585篇 |
2002年 | 523篇 |
2001年 | 159篇 |
2000年 | 174篇 |
1999年 | 194篇 |
1998年 | 144篇 |
1997年 | 108篇 |
1996年 | 89篇 |
1995年 | 89篇 |
1994年 | 78篇 |
1993年 | 90篇 |
1992年 | 112篇 |
1991年 | 96篇 |
1990年 | 108篇 |
1989年 | 87篇 |
1988年 | 85篇 |
1987年 | 68篇 |
1986年 | 54篇 |
1985年 | 68篇 |
1984年 | 58篇 |
1983年 | 51篇 |
1982年 | 39篇 |
1981年 | 43篇 |
1980年 | 38篇 |
1979年 | 41篇 |
1978年 | 48篇 |
1977年 | 39篇 |
1975年 | 37篇 |
1974年 | 33篇 |
1972年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Jeroen M. G. Stevens Hilde Vervaecke Han de Vries Linda van Elsacker 《International journal of primatology》2007,28(6):1417-1430
Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive
bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking
positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate
≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance.
We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are
highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females,
but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity
semidespotic rather than egalitarian. 相似文献
12.
13.
Food sharing: a model of manipulation by harassment 总被引:3,自引:1,他引:2
Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is
in their own self-interestthey avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if
they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic. 相似文献
14.
Mary Margaret Huizinga Sara N. Bleich Mary Catherine Beach Jeanne M. Clark Lisa A. Cooper 《Obesity (Silver Spring, Md.)》2010,18(10):1932-1937
Physician perception of medication adherence may alter prescribing patterns. Perception of patients has been linked to readily observable factors, such as race and age. Obesity shares a similar stigma to these factors in society. We hypothesized that physicians would perceive patients with a higher BMI as nonadherent to medication. Data were collected from the baseline visit of a randomized clinical trial of patient–physician communication (240 patients and 40 physicians). Physician perception of patient medication adherence was measured on a Likert scale and dichotomized as fully adherent or not fully adherent. BMI was the predictor of interest. We performed Poisson regression analyses with robust variance estimates, adjusting for clustering of patients within physicians, to examine the association between BMI and physician perception of medication adherence. The mean (s.d.) BMI was 32.6 (7.7) kg/m2. Forty‐five percent of patients were perceived as nonadherent to medications by their physicians. Higher BMI was significantly and negatively associated with being perceived as adherent to medication (prevalence ratio (PrR) 0.76, 95% confidence interval (CI): 0.64–0.90; P = 0.002; per 10 kg/m2 increase in BMI). BMI remained significantly and negatively associated with physician perception of medication adherence after adjustment for patient and physician characteristics (PrR 0.80, 95% CI: 0.66–0.96; P = 0.020). In this study, patients with higher BMI were less likely to be perceived as adherent to medications by their providers. Physician perception of medication adherence has been shown to affect prescribing patterns in other studies. More work is needed to understand how this perception may affect the care of patients with obesity. 相似文献
15.
16.
17.
Vacuum ultraviolet circular dichroism spectra are reported for poly(galacturonic acid) solution and film, sodium polygalacturonate solution and film, and calcium polygalacturonate gel. In addition to the positive c.d. band near 208 nm previously observed, we find a pair of higher energy bands at 170 180 nm (negative) and 145 nm (positive). The low energy band, assigned to an carboxyl transition, is blue-shifted upon gelation or film formation. 相似文献
18.
Serotyping is the foundation of pathogenic Escherichia coli diagnostics; however, few laboratories have this capacity. We developed a molecular serotyping protocol that targets, genetically, the same somatic and flagellar antigens of E. coli O26:H11 used in traditional serotyping. It correctly serotypes strains untypeable by traditional methods, affording primary laboratories serotyping capabilities. 相似文献
19.
Jake V Bailey Verena Salman Gregory W Rouse Heide N Schulz-Vogt Lisa A Levin Victoria J Orphan 《The ISME journal》2011,5(12):1926-1935
We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization. 相似文献
20.