全文获取类型
收费全文 | 73530篇 |
免费 | 5547篇 |
国内免费 | 145篇 |
出版年
2021年 | 781篇 |
2020年 | 559篇 |
2019年 | 659篇 |
2018年 | 1235篇 |
2017年 | 1143篇 |
2016年 | 1774篇 |
2015年 | 2765篇 |
2014年 | 3052篇 |
2013年 | 3795篇 |
2012年 | 4784篇 |
2011年 | 4460篇 |
2010年 | 2821篇 |
2009年 | 2323篇 |
2008年 | 3715篇 |
2007年 | 3746篇 |
2006年 | 3563篇 |
2005年 | 3467篇 |
2004年 | 3289篇 |
2003年 | 3060篇 |
2002年 | 3031篇 |
2001年 | 1809篇 |
2000年 | 1895篇 |
1999年 | 1579篇 |
1998年 | 777篇 |
1997年 | 604篇 |
1996年 | 558篇 |
1995年 | 496篇 |
1994年 | 536篇 |
1993年 | 481篇 |
1992年 | 980篇 |
1991年 | 925篇 |
1990年 | 928篇 |
1989年 | 842篇 |
1988年 | 795篇 |
1987年 | 717篇 |
1986年 | 666篇 |
1985年 | 651篇 |
1984年 | 610篇 |
1983年 | 535篇 |
1982年 | 489篇 |
1981年 | 464篇 |
1980年 | 354篇 |
1979年 | 560篇 |
1978年 | 427篇 |
1977年 | 363篇 |
1975年 | 410篇 |
1974年 | 415篇 |
1973年 | 366篇 |
1972年 | 394篇 |
1971年 | 345篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Justin C. Luong Patrick L. Turner Celina N. Phillipson Katja C. Seltmann 《Ecological Entomology》2019,44(4):471-479
1. It is hypothesised that ecological restoration in grasslands can induce an alternative stable state shift in vegetation. The change in vegetation influences insect community assemblages and allows for greater functional redundancy in pollination and refuge for native insect species. 2. Insect community assemblages at eight coastal California grassland sites were evaluated. Half of these sites had undergone restoration through active revegetation of native grassland flora and half were non‐restored. Insects were collected from Lupinus bicolor (Fabaceae) within 2 × 2‐m2 plots in spring 2017. Lupinus bicolor is a common native species that is used in California restoration projects, and home and state landscaping projects. 3. Ordination demonstrated that insect community assemblages were different between restored and non‐restored sites. These differences were seen in insect functional groups as well as taxa‐specific differences and were found to be driven by environmental characteristics such as non‐native forb cover. 4. Functional redundancy of herbivores decreased at restored sites, while pollinators became more redundant compared with non‐restored sites. The assemblages of the common species found at restoration sites contained more native insects than those found at non‐restored sites, including species such as Bombus vosnesenskii. 5. Local grassland restoration has the potential to induce an alternative stable state change and affect insect community assemblages. Additionally, it was found that grassland restoration can be a potential conservation tool to provide refugia for bumblebees (Bombus), but additional studies are required to fully understand its broader applicability. 相似文献
32.
33.
Flushing measurements and a resin cast of a burrow inhabited by Sesarma messa and Alpheus cf macklay were taken from a Rhizophoraspp. forest. The burrow had 9 openings and occupied a swamp surface area of 0.64 m2. Passive irrigation of the burrow was investigated by recording change in conductivity of burrow water in a chamber 45 cm below the swamp surface during tidal inundation of the swamp. The chamber was completely flushed within approximately one hour, i.e. by a single tidal event. Burrow morphology was determined by means of resin casting. The investigated burrow was of discrete structure, with an overall depth of 1.2 m and a total volume of 68 l, i.e. ca. 9% of the volume of swamp soil. The below ground surface area of chambers and tunnels was 3.8 m2. The mean and maximum chamber/tunnel diameter was 7 cm and 11 cm respectively. The soil in the close vicinity of the burrow was extensively penetrated by roots, and any two parts of the burrow were located no further than 20 cm away from each other. By reducing diffusion distances within the soil and by being well flushed, the burrows provide an efficient mechanism for removal of excess salt accumulated in the soil around mangrove roots due to exclusion. 相似文献
34.
35.
Christoph D. Dahl Nikos K. Logothetis Heinrich H. Bülthoff Christian Wallraven 《Proceedings. Biological sciences / The Royal Society》2010,277(1696):2973-2981
Primates possess the remarkable ability to differentiate faces of group members and to extract relevant information about the individual directly from the face. Recognition of conspecific faces is achieved by means of holistic processing, i.e. the processing of the face as an unparsed, perceptual whole, rather than as the collection of independent features (part-based processing). The most striking example of holistic processing is the Thatcher illusion. Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 180°), but strikingly grotesque when the face is upright. This effect can be explained by a lack of processing capabilities for locally rotated facial features when the face is turned upside down. Recently, a Thatcher illusion was described in the macaque monkey analogous to that known from human investigations. Using a habituation paradigm combined with eye tracking, we address the critical follow-up questions raised in the aforementioned study to show the Thatcher illusion as a function of the observer''s species (humans and macaques), the stimulus'' species (humans and macaques) and the level of perceptual expertise (novice, expert). 相似文献
36.
C L Rümke 《Blood cells》1985,11(1):137-140
Ratios of two percentages observed in differential counts of leukocytes or lymphocytes are very imprecise if they are based on relatively small numbers of cells. This is shown by the length of the 95% confidence intervals for such ratios. A formula is given for computing the limits of such intervals. They should accompany each observed value for a ratio. 相似文献
37.
Jürgen Sühnel 《Bulletin of mathematical biology》1998,60(2):197-213
A possible experimental design for combination experiments is to compare the doseresponse curve of a single agent with the
corresponding curve of the same agent using either a fixed amount of a second one or a fixed dose ratio. No interaction is
then often defined by a parallel shift of these curves. We have performed a systematic study for various types of doseresponse
relations both for the dose-additivity (Loewe additivity) and for the independence (Bliss independence) criteria for defining
zero interaction. Parallelism between doseresponse curves of a single agent and those of the same agent in the presence of
a fixed amount of another one is found for the Loewe-additivity criterion for linear doseresponse relations. For nonlinear
relations, one has to differentiate between effect parallelism (parallel shift on the effect scale) and dose parallelism (parallel
shift on the dose scale). In the case of Loewe additivity, zero-interaction dose parallelism is found for power, Weibull,
median-effect and logistic doseresponse relations, given that special parameter relationships are fulfilled. The mechanistic
model of competitive interaction exhibits dose parallelism but not effect parallelism for Loewe additivity. Bliss independence
and Loewe additivity lead to identical results for exponential doseresponse curves. This is the only case for which dose parallelism
was found for Bliss independence. Parallelism between single-agent doseresponse relations and Loewe additivity mixture relations
is found for examples with a fixed doseratio design. However, this is again not a general property of the design adopted but
holds only if special conditions are fulfilled. The comparison of combination doseresponse curves with single-agent relations
has to be performed taking into account both potency and shape parameters. The results of this analysis lead to the conclusion
that parallelism between zero interaction combination and single-agent doseresponse relations is found only for special cases
and cannot be used as a general criterion for defining zero-interaction in combined-action assessment even if the correct
potency shift is taken into account. 相似文献
38.
The results of recent randomized trials to test the influence of antioxidants on coronary-event rates and prognosis in patients
with coronary-artery disease were disappointing. In none of these studies did the use of vitamin E improve prognosis. In contrast,
treatment of coronary-artery disease with angiotensin-converting-enzyme (ACE) inhibitors reduced coronary-event rates and
improved prognosis. ACE inhibition prevents the formation of angiotensin II, which has been shown to be a potent stimulus
of superoxide-producing enzymes in atherosclerosis. The findings suggest that inhibition of superoxide production at enzymatic
levels, rather than symptomatic superoxide scavenging, may be the better choice of treatment. 相似文献
39.
Detection of genetic variants affecting cattle behaviour and their impact on milk production: a genome‐wide association study
下载免费PDF全文
![点击此处可从《Animal genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Juliane Friedrich Bodo Brand Siriluck Ponsuksili Katharina L. Graunke Jan Langbein Jacqueline Knaust Christa Kühn Manfred Schwerin 《Animal genetics》2016,47(1):12-18
Behaviour traits of cattle have been reported to affect important production traits, such as meat quality and milk performance as well as reproduction and health. Genetic predisposition is, together with environmental stimuli, undoubtedly involved in the development of behaviour phenotypes. Underlying molecular mechanisms affecting behaviour in general and behaviour and productions traits in particular still have to be studied in detail. Therefore, we performed a genome‐wide association study in an F2 Charolais × German Holstein cross‐breed population to identify genetic variants that affect behaviour‐related traits assessed in an open‐field and novel‐object test and analysed their putative impact on milk performance. Of 37 201 tested single nucleotide polymorphism (SNPs), four showed a genome‐wide and 37 a chromosome‐wide significant association with behaviour traits assessed in both tests. Nine of the SNPs that were associated with behaviour traits likewise showed a nominal significant association with milk performance traits. On chromosomes 14 and 29, six SNPs were identified to be associated with exploratory behaviour and inactivity during the novel‐object test as well as with milk yield traits. Least squares means for behaviour and milk performance traits for these SNPs revealed that genotypes associated with higher inactivity and less exploratory behaviour promote higher milk yields. Whether these results are due to molecular mechanisms simultaneously affecting behaviour and milk performance or due to a behaviour predisposition, which causes indirect effects on milk performance by influencing individual reactivity, needs further investigation. 相似文献
40.
DNA was efficiently and quantitatively isolated from extremely small quantities of mycelia (0.1–10 mg) of different phytopathogenic
moulds by grinding freeze-dried mycelia with glass beads and then using a commercial DNA extraction kit. The efficiency of
disruption of the mycelia and the quantitative DNA extraction was proved by microscopy and the quantification of isolated
DNA by real time PCR.
Presented at the 27th Mykotoxin-Workshop, Dortmund, Germany, June 13–15, 2005
Financial support: German Research Foundation (DFG grant Pr 708/2). J.M. thanks the Cusanuswerk for a doctoral scholarship 相似文献