全文获取类型
收费全文 | 3411篇 |
免费 | 217篇 |
出版年
2022年 | 16篇 |
2021年 | 33篇 |
2019年 | 28篇 |
2018年 | 38篇 |
2017年 | 35篇 |
2016年 | 78篇 |
2015年 | 92篇 |
2014年 | 130篇 |
2013年 | 133篇 |
2012年 | 224篇 |
2011年 | 246篇 |
2010年 | 187篇 |
2009年 | 140篇 |
2008年 | 187篇 |
2007年 | 187篇 |
2006年 | 166篇 |
2005年 | 173篇 |
2004年 | 151篇 |
2003年 | 175篇 |
2002年 | 158篇 |
2001年 | 39篇 |
2000年 | 27篇 |
1999年 | 58篇 |
1998年 | 58篇 |
1997年 | 45篇 |
1996年 | 60篇 |
1995年 | 40篇 |
1994年 | 43篇 |
1993年 | 33篇 |
1992年 | 51篇 |
1991年 | 30篇 |
1990年 | 42篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 32篇 |
1980年 | 21篇 |
1979年 | 34篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1971年 | 15篇 |
1970年 | 16篇 |
1969年 | 13篇 |
1967年 | 14篇 |
排序方式: 共有3628条查询结果,搜索用时 31 毫秒
71.
Manfred J. Sippl 《Proteins》1993,17(4):355-362
A major problem in the determination of the three-dimensional structure of proteins concerns the quality of the structural models obtained from the interpretation of experimental data. New developments in X-ray crystallography and nuclear magnetic resonance spectroscopy have acceleratedd the process of structure determination and the biological community is confronted with a steadily increasing number of experimentally determined protein folds. However, in the recent past several experimentally determined protein structures have been proven to contain major errors, indicating that in some cases the interpretation of experimental data is difficult and may yield incorrect models. Such problems can be avoided when computational methods are employed which complement experimental structure determinations. A prerequisite of such computational tools is that they are independent of the parameters obtained from a particular experiment. In addition such techniques are able to support and accelerate experimental structure determinations. Here we present techniques based on knowledge based mean fields which can be used to judge the quality of protein folds. The methods can be used to identify misfolded structures as well as faulty parts of structural models. The techniques are even applicable in cases where only the Cα trace of a protein conformation is available. The capabilities of the technique are demonstrated using correct and incorrect protein folds. © 1993 Wiley-Liss, Inc. 相似文献
72.
Hartmut B. Stegmann Manfred Murer Ulrike Hfler Klaus Scheffler Frank Hewgill 《Chirality》1993,5(4):282-287
Chiral recognition with magnetic methods requires the formation of diastereomers. Due to the variety of appropriate reactions, hydrogen bond formation, esterification, and acetalization as well as host–guest interactions were chosen for basic investigations. The results obtained indicate that in the case of diamagnetic compounds the chemical shifts and for paramagnetic compounds the β-proton coupling constants are the most useful parameters. By combination of both pieces of information, assignment of the absolute configuration was achieved. © 1993 Wiley-Liss, Inc. 相似文献
73.
74.
Manfred Rösch 《Vegetation History and Archaeobotany》1993,2(4):213-232
The second part of a pollen profile from Hornstaad/Lake Constance (Germany), containing the Atlantic and Subboreal (6400 cal B.C. to 700 cal B.C.) is presented. The diagram has a sampling interval of 1 cm and an average time resolution of 10 years. The cereal curve provided the basis for cereal zones, which are used to classify the human impact. Twenty-six cereal zones can be distinguished, most of them divided into subzones, from 5500 cal B.C. to 700 cal B.C. They correspond to both known and, mostly, unknown settlements in the surrounding landscape from the Early Neolithic to the Late Bronze Age. Charcoal and chemical analyses as well as sediment accumulation, confirmed by accelerator dates, provide evidence for human impact on the environment.A contribution to the 8th IPC, Aix-en-Provence, Sept. 1992 相似文献
75.
C. Born M. Biselli C. Wandrey J. Thömmes M. -R. Kula 《Bioprocess and biosystems engineering》1996,15(1):21-29
Continuous culture may be an efficient way of producing proteins which are susceptible to secondary processing in the course of a fermentation process. Short residence times in these systems support the production of correctly assembled proteins by avoiding substrate limitations and product inhibitions and also minimize the contact of sensitive bioproducts with degrading enzymes. Thus products of increased stability and integrity are obtained from continuous processes. The downstream process following continuous culture has to be adapted to the specific conditions of continuous fermentations, e.g. large liquid volumes and diluted process solutions. In this paper an approach is shown how a fluidized bed adsorption as first recovery operation may be coupled directly to a continuous production. Immobilized hybridoma cells are cultivated in porous glass microcarriers in a continuous fluidized bed process, the cell containing harvest is purified by fluidized bed adsorption using an agarose based cation exchange matrix. By this coupled mode of operation the large biomass containing harvest volume resulting from the continuous cultivation may be applied directly to a fluidized chromatographic matrix without prior clarification, leading to a particle free and initially purified product solution of reduced volume. In an experimental setup a bench-scale fluidized bed bioreactor of 25 ml carrier volume was coupled to a fluidized bed adsorption column operated with 300 ml of adsorbent. This configuration yielded up to 20 mg of monoclonal antibody per day in a cell free solution at fourfold concentration and fivefold purification. The process was run for more than three weeks with consistent product output.The help of H. Schmitz, A. Bader, J. Gätgens and M. Halfar during the experiments is gratefully acknowledged. This work was partially funded by the ministry of science and research of the Federal Republic of Germany within the project Stoffumwandlung mit Biokatalysatoren. 相似文献
76.
The present study was conducted to investigate the effect of zinc deficiency on fatty acid desaturation in rats fed two different
types of dietary fat, a mixture of coconut oil and safflower oil (7∶1, w/w, “coconut oil diet”) or linseed oil (“linseed oil
diet”). In order to ensure an adequate food intake, all rats were force-fed by gastric tube. Zinc deficiency caused statistical
significant reducion of Δ9-desaturase activity in liver microsomes of rats fed coconut oil diet and tendencial reduction (p<0.15) in rats fed linseed oil diet compared with control rats fed diets with the same type of fat. In agreement with this
effect, zinc deficiency in the rats fed both types of dietary fat increased the ratio between total saturated and total monounsaturated
fatty in liver phospholipids and liver microsomes. Zinc deficient rats on the coconut oil diet had unchanged Δ6-desaturase
activity with linoleic acid as substrate and lowered activity with α-linolenic acid as substrate. In contrast, zinc deficient
rats on the linseed oil diet had increased Δ6-desaturase activity with linoleic acid as substrate and unchanged activity with
α-linolenic acid. Because linoleic acid is the main substrate for Δ6-desaturase in the rats fed coconut oil diet, and α-linolenic
acid is the main substrate in the rats fed linseed oil diet, it is concluded that in vivo Δ6-desaturation was not changed
by zinc deficiency in the rats fed both types of dietary fat. Activity of Δ5-desaturase was also not changed by zinc deficiency
in the rats fed both dietary fats. Levels of fatty acids in liver phospholipids and microsomes derived by Δ4-, Δ5-, and Δ6-desaturation
were not consistently changed by zinc deficiency in the rats fed both types of dietary fat. Thus, the enzyme studies and also
fatty acid composition data of liver phospholipids and microsomes indicate that zinc deficiency does not considerably disturb
desaturation of linoleic and α-linolenic acid. Therefore, it is suggested that similarities between deficiencies of zinc and
essential fatty acids described in literature are not due to disturbed desaturation of linoleic acid in zinc deficiency. The
present study also indicates that zinc deficiency enhances incorporation of eicosapentaenoic acid into phosphatidylcholine
of rats fed diets with large amounts ofn-3 polyunsaturated fatty acids. 相似文献
77.
Manfred Heinlein 《Molecular & general genetics : MGG》1995,246(1):1-9
The Ac elements present in the unstable wxm7 and wx-m9 alleles of maize trigger different patterns of Ds excision in trans. To determine whether this differential regulation is a feature of the Ac alleles themselves or is mediated by genetically distinct factors, maize plants heterozygous for the wx-m7 and wx-m9 alleles were crossed to tester strains homozygous for Ds reporter alleles. Kernels showing the variegation pattern characteristic for the Ac elements carried in the wx-m7 and wx-m9 alleles were found to be present in the ratios expected from the genetic constitution of the strains. The aleurone variegation caused by excision of the Ds reporter element and the endosperm variegation caused by excision of Ac from the wx-m7 and wx-m9 alleles themselves segregated with the original wx-m alleles. In addition, stable Wx and wx derivatives of wx-m9 that have lost Ac no longer exert any trans effect on the wx-m7 allele (and vice versa). Therefore it is concluded that the observed variegation patterns are autonomously determined by specific trans effects of the particular Ac element. 相似文献
78.
79.
van der Pol JJ Machnik M Biselli M Portela-Klein T de Gooijer CD Tramper J Wandrey C 《Cytotechnology》1997,24(1):19-30
The monoclonal-antibody production of an immobilized hybridoma cell line cultivated in a fluidized-bed reactor was monitored
on-line for nearly 900 h. The monoclonal antibody concentration was determined by an immuno affinity-chromatography method
(ABICAP). Antibodies directed against the product, e.g. IgG, were immobilized on a micro-porous gel and packed in small columns.
After all IgG present in the sample was bound to the immobilized antibodies, unbound proteins were removed by rinsing the
column. Elution of the bound antibodies followed and the antibodies were determined by fluorescence. The analytical procedure
was automated with a robotic device to enable on-line measurements. The correlation between the on-line determined data and
antibody concentrations measured by HPLC was linear.
A sampling system was constructed, which was based on a pneumatically actuated in-line membrane valve integrated into the
circulation loop of the reactor. Separation of the cells from the sample stream was achieved by a depth filter made of glass-fibre,
situated outside the reactor. Rapid obstruction of the filter by cells or cell debris and contamination of the sample system
was avoided by intermittent rinsing of the sample system with a chemical solution. The intermittent rinsing of the filter,
which had a surface of 4.8 cm2, resulted in an operational capacity of up to 40 samples (1.0 l total sample volume). Both the sampling system and the analytical
device functioned without failure during this long-term culture.
The culture temperature was varied between 34 and 40 °C. Raising the temperature from 34 up to 37 °C resulted in a simultaneous
increase of growth and specific antibody production rate. Specific metabolic rates of glucose, lactate, glutamine and ammonium
stayed constant in this temperature range. A further enhancement of temperature up to 40 °C had a negative effect on the growth
rate, whereas the specific monoclonal antibody production rate showed a small increase. The other specific metabolic rates
also increased in the temperature range between 38 to 40 °C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.