全文获取类型
收费全文 | 2753篇 |
免费 | 237篇 |
国内免费 | 2篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 37篇 |
2021年 | 86篇 |
2020年 | 45篇 |
2019年 | 66篇 |
2018年 | 76篇 |
2017年 | 86篇 |
2016年 | 88篇 |
2015年 | 156篇 |
2014年 | 157篇 |
2013年 | 216篇 |
2012年 | 199篇 |
2011年 | 212篇 |
2010年 | 132篇 |
2009年 | 128篇 |
2008年 | 178篇 |
2007年 | 212篇 |
2006年 | 183篇 |
2005年 | 158篇 |
2004年 | 153篇 |
2003年 | 116篇 |
2002年 | 132篇 |
2001年 | 16篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2992条查询结果,搜索用时 15 毫秒
1.
Formaldehyde fixation of cells is routinely used to study DNA-protein interactions in vivo. In these studies, DNA is often analyzed using a polymerase chain reaction technique. Although it is known that formaldehyde can damage DNA, no studies have been performed so far to compare the efficiency of DNA amplification between normal and fixed cells. Here we show that formaldehyde fixation results in a 15% to 20% reduction in the ability to amplify cellular DNA. The loss of amplifiability is independent of the length of the amplification region and the degree to which DNA is compacted on packaging into chromatin. 相似文献
2.
L L Korsun E Koluvamioko J Vembe 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(10):32-35
The influence of proteolytic enzymes on the increase of the sensitivity of cell cultures to Newcastle disease virus was tested in the continuous culture of goat embryo kidney cells. In this investigation the dose of trypsin and the time of incubation for the treatment of the cell culture was selected. The preliminary treatment of the monolayer culture of goat embryo kidney cells with trypsin by incubation at a temperature of 18-20 degrees C for 30 minutes made it possible to increase the sensitivity of the culture to Newcastle disease virus 10-fold. 相似文献
3.
Sergey V. Budaev 《Ethology : formerly Zeitschrift fur Tierpsychologie》2010,116(5):472-480
Principal component (PCA) and factor analysis (FA) are widely used in animal behaviour research. However, many authors automatically follow questionable practices implemented by default in general‐purpose statistical software. Worse still, the results of such analyses in research reports typically omit many crucial details which may hamper their evaluation. This article provides simple non‐technical guidelines for PCA and FA. A standard for reporting the results of these analyses is suggested. Studies using PCA and FA must report: (1) whether the correlation or covariance matrix was used; (2) sample size, preferably as a footnote to the table of factor loadings; (3) indices of sampling adequacy; (4) how the number of factors was assessed; (5) communalities when sample size is small; (6) details of factor rotation; (7) if factor scores are computed, present determinacy indices; (8) preferably they should publish the original correlation matrix. 相似文献
4.
5.
Chantal N. van Dijk Merel van Witteloostuijn Nada Vasi? Sergey Avrutin Elma Blom 《PloS one》2016,11(3)
When sending text messages on their mobile phone to friends, children often use a special type of register, which is called textese. This register allows the omission of words and the use of textisms: instances of non-standard written language such as 4ever (forever). Previous studies have shown that textese has a positive effect on children’s literacy abilities. In addition, it is possible that children’s grammar system is affected by textese as well, as grammar rules are often transgressed in this register. Therefore, the main aim of this study was to investigate whether the use of textese influences children’s grammar performance, and whether this effect is specific to grammar or language in general. Additionally, studies have not yet investigated the influence of textese on children’s cognitive abilities. Consequently, the secondary aim of this study was to find out whether textese affects children’s executive functions. To investigate this, 55 children between 10 and 13 years old were tested on a receptive vocabulary and grammar performance (sentence repetition) task and various tasks measuring executive functioning. In addition, text messages were elicited and the number of omissions and textisms in children’s messages were calculated. Regression analyses showed that omissions were a significant predictor of children’s grammar performance after various other variables were controlled for: the more words children omitted in their text messages, the better their performance on the grammar task. Although textisms correlated (marginally) significantly with vocabulary, grammar and selective attention scores and omissions marginally significantly with vocabulary scores, no other significant effects were obtained for measures of textese in the regression analyses: neither for the language outcomes, nor for the executive function tasks. Hence, our results show that textese is positively related to children’s grammar performance. On the other hand, use of textese does not affect—positively nor negatively—children’s executive functions. 相似文献
6.
Yoko Yamauchi Hikari Kimoto Xianyu Yang Sergey Filkin Yuri Utkin Tai Kubo 《Bioscience, biotechnology, and biochemistry》2016,80(1):158-161
Three-finger toxins (3FTxs) are one of the major components in snake venoms. In this study, we isolated a cDNA encoding a short-chain 3FTx, Pr-SNTX, from Pseudechis rossignolii. The amino acid sequence of Pr-SNTX is nearly identical to that of its ortholog in Pseudechis australis. Pr-SNTX protein inhibited muscle-type (α2βδε), but not neuronal α7 nicotinic acetylcholine receptor (nAChR) activity. 相似文献
7.
N S Korsun D N Nosik A S Novokhatski? G N Trushinskaia 《Antibiotiki i khimioterapii͡a》1988,33(11):827-830
Preparation of highly active rabbit antisera (AS) to human recombinant alpha 2-interferon and their use for studying biological properties of natural and plasmid alpha-interferons are described. By exhaustion of AS by alpha 3-interferon there were prepared practically monospecific AS not reacting with antigenic determinants of alpha 3-interferon. It was found that alpha 3-interferon represented a significant portion of human lymphoblastoid interferons and was included in PH-labile alpha-interferon from serum of patients with Kaposi carcinoma. AS to alpha 2-interferon completely neutralized antiviral and antiproliferative activity of the homologous subtype alpha-interferon and stimulation of cytotoxicity of human natural killer cells induced by it. It neutralized also the same effects of the heterologous subtypes (alpha 3 and alpha F/D) and leukocytic interferon, but the neutralization level was lower. The results of the study confirmed the polyfunctional nature of the interferon molecule. 相似文献
8.
Sergey Kh. Degtyarev 《FEBS letters》1983,154(2):293-296
Smooth muscle cell energetics of taenia caeci during relaxation, activity and maximal contraction were investigated using 31P-NMR. In relaxed muscle obtained in calcium-free medium, [ATP], [phosphocreatine] and [sugar phosphate] were 4.4 mM, 7.7 mM and 2.8 mM, respectively. There was only a small difference in the energetics of spontaneously active and maximally contracted muscles, but under both conditions substantial changes occurred as compared with relaxed muscles. The internal pH in relaxed muscle was found to be 7.05, which acidified to 6.5 during contraction. The level of sugar phosphates was found to be not a limiting factor in energetics. 相似文献
9.
The deterministic model of microevolutionary dynamics of “phagebacteria” ecosystem is analyzed. Primary (and after all decisive) events that determine the dynamics are direct interactions between bacterial reception and viral adsorption proteins. Structure of the model is that under real parameters of adsorption, lysis and reproduction each separate (ith) stage of microevolution comes to end with total lysis of ith population of bacteria by ith population of phage. It is shown however that in the course of joint microevolution both populations pass over some critical sizes when a new pair of antagonistic strains arises with certainty from mutations. As a result it is easy to visualize and simulate by computer the process of successive fixations of such pairs of mutants. This coevolution is the original example of a locally adaptive but globally undirected process which is characterized also by: (1) constant average rate, (2) neutrality of mutations at the moment of their emergence and during the period of “anticipation” of ecological changes, (3) pure adaptivity of the same mutations at the moment of proper fixation and (4) “intrinsic origin” (from the ecosystem dynamics itself) of selective constraints. 相似文献
10.
Marco Patacca Marcus Lindner Manuel Esteban Lucas-Borja Thomas Cordonnier Gal Fidej Barry Gardiner Ylva Hauf Gediminas Jasinevičius Sophie Labonne Edgaras Linkevičius Mats Mahnken Slobodan Milanovic Gert-Jan Nabuurs Thomas A. Nagel Laura Nikinmaa Momchil Panyatov Roman Bercak Rupert Seidl Masa Zorana Ostrogović Sever Jaroslaw Socha Dominik Thom Dijana Vuletic Sergey Zudin Mart-Jan Schelhaas 《Global Change Biology》2023,29(5):1359-1376
Over the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long-term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground-based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m3 of disturbed timber volume per year over the 70-year study period. This value is likely a conservative estimate due to under-reporting, especially of small-scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m3/year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long-term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes. 相似文献