全文获取类型
收费全文 | 1917篇 |
免费 | 183篇 |
国内免费 | 5篇 |
出版年
2022年 | 15篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 62篇 |
2014年 | 70篇 |
2013年 | 91篇 |
2012年 | 95篇 |
2011年 | 119篇 |
2010年 | 62篇 |
2009年 | 49篇 |
2008年 | 77篇 |
2007年 | 103篇 |
2006年 | 91篇 |
2005年 | 96篇 |
2004年 | 70篇 |
2003年 | 76篇 |
2002年 | 66篇 |
2001年 | 58篇 |
2000年 | 51篇 |
1999年 | 58篇 |
1998年 | 29篇 |
1997年 | 14篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 28篇 |
1992年 | 33篇 |
1991年 | 27篇 |
1990年 | 34篇 |
1989年 | 27篇 |
1988年 | 19篇 |
1987年 | 30篇 |
1986年 | 25篇 |
1985年 | 27篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 18篇 |
1972年 | 11篇 |
排序方式: 共有2105条查询结果,搜索用时 31 毫秒
161.
Complete inventories of kinesins from three pathogenic filamentous ascomycetes, Botryotinia fuckeliana, Cochliobolus heterostrophus, and Gibberella moniliformis, are described. These protein sequences were compared with those of the filamentous saprophyte, Neurospora crassa and the two yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. Data mining and phylogenetic analysis of the motor domain yielded a constant set of 10 kinesins in the filamentous fungal species, compared with a smaller set in S. cerevisiae and S. pombe. The filamentous fungal kinesins fell into nine subfamilies when compared with well-characterized kinesins from other eukaryotes. A few putative kinesins (one in B. fuckeliana and two in C. heterostrophus) could not be defined as functional, due to unorthodox organization and lack of experimental data. The broad representation of filamentous fungal kinesins across most of the known subfamilies and the ease of gene manipulation make fungi ideal models for functional and evolutionary investigation of these proteins. 相似文献
162.
Peisen?ZhangEmail author Huitao?Sheng Alfredo?Morabia T?Conrad?Gilliam 《BMC bioinformatics》2003,4(1):3
Background
Haplotype based linkage disequilibrium (LD) mapping has become a powerful and cost-effective method for performing genetic association studies, particularly in the search for genetic markers in linkage disequilibrium with complex disease loci. Various methods (e.g. Monte-Carlo (Gibbs sampling); EM (expectation maximization); and Clark's method) have been used to estimate haplotype frequencies from routine genotyping data. 相似文献163.
Jessica?Lagerstedtkth.se" title="jessica@md kth.se" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author Conrad?Luttropp Lars-Gunnar?Lindfors 《The International Journal of Life Cycle Assessment》2003,8(3):160-166
Aim, Scope and Background The interest in environmental questions has increased enormously during the last decade. Environmental protection has become
an issue of strategic importance within the manufacturing industry and many companies are now working in the field of Design
for Environment (DFE). The main purpose of DFE is to create products and services for achieving a sustainable society. Designers
are widely believed to have a key role in adapting products to a sustainable society and one of the major instruments in the
context of Design for Environment is Life Cycle Assessment (LCA). However, product development creates particular challenges
for incorporating environmental issues that combine functional and environmental assessment. A natural and important part
of product design is to define and analyse the functions of the product. Consequently, the functional unit in LCA is a core
issue in DFE. Most recent research in DFE has focused on how to reduce the environmental impact of products throughout their
life-cycle by addressing environmental aspects, while little attention has been given to the functionality of the product.
Additionally, early product development phases, so called re-think phases, are considered to have the influence on major changes
in products in general. These phases have thus the highest potential for changing products and product systems towards a sustainable
development.
Main Features This paper discusses an extended functional representation in design for environment methods to evaluate sustainable design
solutions, especially in early (re-think) phases of product design. Based on engineering-design science and several case studies,
a concept has been developed describing how functional preferences can be visualised in design for environment and product
development. In addition, the functional unit in LCA is discussed. The concept is called Functional Profile (FP) and is additionally
exemplified in a case study on radio equipment.
Discussion The new functional characterisation concept helps identify functional priorities in design for environment. The Functional
Profile is a structured, systematic and creative concept for identifying the necessary functions of a new product. The FP
is envisioned to complement existing design for environment methods, not to replace them. Instead of being a product-development
tool or method, the concept is an approach that increases understanding of inter-reactions between functional characteristics
of products and their environmental characteristics, which furthermore facilitates trade-off decisions. One of the objectives
behind the concept is to highlight the importance of balancing functional requirements and environmental impacts, presenting
both the advantages and disadvantages of the product.
Outlook A second paper will be produced to complement the functional-environmental characterisation concept in early product development
phase, presenting the environmental characterisation part and illustrating correlations between the functional and environmental
sides. 相似文献
164.
Conrad M 《Bio Systems》2001,60(1-3):23-38
Issues addressed in H.H. Pattee's origin of life laboratory in the 1960s and their connection to the physics–evolution–language problematic are indicated. The problem of quantum measurement played a central role. The problem is herein examined in the light of the fluctuon model; in particular, as the model applies to gravity. The main conclusion is that measurement and motion are a unitary process. All accelerations are accompanied by a cycle involving the annihilation and creation of superpositions. Gravitational collapse is also a cyclic process in the fluctuon model. By a suitable transformation, it can be seen that interactions underlying superpositional collapse are the same as those operative in gravitational collapse. Implications for the origin of cellular life and the development of symbolic systems are considered. 相似文献
165.
Conrad CC Grabowski DT Walter CA Sabia M Richardson A 《Free radical biology & medicine》2000,28(3):447-462
Mice with null mutations for metallothionein genes MT-1 and MT-2 were used to study the role that metallothionein plays in protecting cellular targets in vivo from oxidative stress. Wild-type (MT(+/+)) and MT-null (MT(-/-)) mice were treated with either saline or zinc and exposed to two types of oxidative stress: gamma-irradiation or 2-nitropropane. There was no alteration in the antioxidant defense system (superoxide dismutase, catalase, or glutathione peroxidase and glutathione levels) to compensate for the lack of the metallothionein in the MT(-/-) mice. The amount of oxidative damage to liver DNA, lipids, and proteins were similar for the MT(-/-) and MT(+/+) mice even though the levels of metallothionein in the livers of the saline- or zinc-pretreated MT(+/+) mice were 5- to 100-fold greater than found in the MT(-/-) mice. To determine if metallothionein can protect mice from the lethal effects of ionizing radiation, the mean survivals of MT(-/-) and MT(+/+) mice exposed to whole body gamma-irradiation were measured and found to be similar. However, the mean survival increased significantly after zinc pretreatment for both the MT(-/-) and MT(+/+) mice. These results demonstrate that tissue levels of metallothionein do not protect mice in vivo against oxidative stress. 相似文献
166.
167.
When cells of a type II methanotrophic bacterium (Methylocystis strain LR1) were starved of methane, both the K(m(app)) and the V(max(app)) for methane decreased. The specific affinity (a(o)(s)) remained nearly constant. Therefore, the decreased K(m(app)) in starved cells was probably not an adjustment to better utilize low-methane concentrations. 相似文献
168.
Effects of O2 and CH4 on presence and activity of the indigenous methanotrophic community in rice field soil 总被引:1,自引:0,他引:1
The activity and distribution of methanotrophs in soil depend on the availability of CH4 and O2. Therefore, we investigated the activity and structure of the methanotrophic community in rice field soil under four factorial combinations of high and low CH4 and O2 concentrations. The methanotrophic population structure was resolved by denaturant gradient gel electrophoresis (DGGE) with different PCR primer sets targeting the 16S rRNA gene, and two functional genes coding for key enzymes in methanotrophs, i.e. the particulate methane monooxygenase (pmoA) and the methanol dehydrogenase (mxaF). Changes in the biomass of type I and II methanotrophic bacteria in the rice soil were determined by analysis of phospholipid-ester-linked fatty acid (PLFA) biomarkers. The relative contribution of type I and II methanotrophs to the measured methane oxidation activity was determined by labelling of soil samples with 14CH4 followed by analysis of [14C]-PLFAs. CH4 oxidation was repressed by high O2 (20.5%), and enhanced by low O2 (1%). Depending on the CH4 and O2 mixing ratios, different methanotrophic communities developed with a higher diversity at low than at high CH4 concentration as revealed by PCR-DGGE. However, a prevalence of type I or II populations was not detected. The [14C]-PLFA fingerprints, on the other hand, revealed that CH4 oxidation activity was dominated by type I methanotrophs in incubations with low CH4 mixing ratios (1000 p.p.m.v.) and during initiation of CH4 consumption regardless of O2 or CH4 mixing ratio. At high methane mixing ratios (10 000 p.p.m.v.), type I and II methanotrophs contributed equally to the measured CH4 metabolism. Collectively, type I methanotrophs responded fast and with pronounced shifts in population structure and dominated the activity under all four gas mixtures. Type II methanotrophs, on the other hand, although apparently more abundant, always present and showing a largely stable population structure, became active later and contributed to CH4 oxidation activity mainly under high CH4 mixing ratios. 相似文献
169.
170.
利用放射性同位素示踪技术研究了14C标记菲在有控系统中的迁移转化。结果表明,14C-菲在有控系统中降解较快,施入药品24d后仅有0.32%的14C-菲存留在植物、营养液和火山石中。植物吸收的14C放射性大部分被结合到植物组织中,其它14C主要以菲的极性代谢物形态存在。 相似文献