全文获取类型
收费全文 | 23336篇 |
免费 | 1568篇 |
国内免费 | 3篇 |
出版年
2023年 | 155篇 |
2022年 | 168篇 |
2021年 | 663篇 |
2020年 | 427篇 |
2019年 | 497篇 |
2018年 | 729篇 |
2017年 | 618篇 |
2016年 | 935篇 |
2015年 | 1398篇 |
2014年 | 1527篇 |
2013年 | 1910篇 |
2012年 | 2226篇 |
2011年 | 2082篇 |
2010年 | 1289篇 |
2009年 | 1102篇 |
2008年 | 1405篇 |
2007年 | 1316篇 |
2006年 | 1267篇 |
2005年 | 1053篇 |
2004年 | 962篇 |
2003年 | 880篇 |
2002年 | 787篇 |
2001年 | 157篇 |
2000年 | 126篇 |
1999年 | 145篇 |
1998年 | 182篇 |
1997年 | 142篇 |
1996年 | 111篇 |
1995年 | 85篇 |
1994年 | 91篇 |
1993年 | 66篇 |
1992年 | 58篇 |
1991年 | 39篇 |
1990年 | 39篇 |
1989年 | 34篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 11篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
F. Perestelo M. A. Falcón Ana Carnicero Ana Rodríguez G. de la Fuente 《Biotechnology letters》1994,16(3):299-302
Summary
Serratia marcescens was found to degrade kraft lignin by only 15%. When 14C-radiolabelled lignocelluloses and DHP lignins were used as substrates the bacterium mineralized to 14CO2 only 1.1–1.9% and 0.4–0.8% of the lignins respectively. However, some 44.4% of the 14C--DHP lignin was recovered as soluble radiolabelled products. 相似文献
102.
The early stages of development of three blenniid species, Aidablennius sphynx (6.7–15.8 mm BL), Coryphoblennius galerita (4.3–13.9mm BL), and Lipophrys canevai (3.5–10.4 mm BL) are described from specimens collected in the western Mediterranean. The characteristics used for identification included meristic, developmental, morphological and pigmentation characters. Distinguishing characters of these species useful in differentiating them from other species of blenniids for which early stages are known in the Mediterranean are presented. Information on the occurrence of larvae and juveniles of these species off the Catalan coast (north-western Mediterranean) is also given. 相似文献
103.
Frida E. Kleiman Raquel Dodelson de Kremer Ana Oller de Ramirez Roy A. Gravel Carlos E. Argaraña 《Human genetics》1994,94(3):279-282
The level of -hexosaminidase activity in plasma and leukocytes and the frequency of three known HEXB mutations were studied in an Argentinean deme with high incidence of infantile Sandhoff disease. Two mutations were previously identified in one of two Sandhoff patients from the region, a splice mutation, IVS-2+1 GA, and a 4-bp deletion, CTTT782–785. These mutations, and a 16kb deletion from the 5' end of the HEXB gene common in non-Argentineans, were screened in 9 Sandhoff patients (all unrelated), 24 obligate heterozygotes, 33 additional individuals belonging to families with affected members, and 64 randomly ascertained individuals from the high risk region. Of 31 independent alleles examined, including those of the two patients previously reported, 30 had the IVS-2 splice mutation and only the originally reported patient had the CTTT deletion. The 16-kb deletion was not observed. Further, among the 57 unaffected members of families with a previous history of Sandhoff disease, and absolute correlation was found between carrier diagnosis by enzyme assay of leukocytes and the DNA-based tests for mutation. One of the 64 controls was classified as a carrier by enzyme assay but did not have one of the three mutations screened. We conclude that a single mutation predominates in this Argentinean population and that the DNA-based test can be an effective supplement or alternative to enzyme-based testing. 相似文献
104.
Elena P. Sawin Laurence R. Harris Ana R. Campos Marla B. Sokolowski 《Journal of Insect Behavior》1994,7(4):553-567
In this paper we examine theDrosophila melanogaster larval response to light. We survey the morphology of the larval visual and motor systems in relation to larval locomotory behavior and phototaxis. In addition, this paper proposes a model of sensorimotor transformation and examines the reversal in taxis occurring at theD. melanogaster larval wnadering stage. 相似文献
105.
Sally J. Grieb Stephen A. Matlin Joseph G. Phillips Ana M. Belenguer Harald J. Ritchie 《Chirality》1994,6(2):129-134
The effect of particle size and pore size of the aminopropylated silica support for cellulose tris(phenylcarbamate) and tris(3,5-dimethylphenylcarbamate) chiral HPLC phases was investigated. It was necessary to reduce phase loading below 20% w/w as pore size and particle size were reduced, but high efficiency columns could be prepared at a 15% w/w loading on 5 and 2.5 μm supports with 120-Å-diameter pores. The 2.5 μm phase permits the use of relatively high flow rates and very efficient enantioselective separations of a range of chiral compounds could be achieved in less than 3 min. © 1994 Wiley-Liss, Inc. 相似文献
106.
Summary Thirty-three insertions of transposon Tn10l6l7 into genes involved in the control of rod cell shape were isolated in Salmonella typhimurium by the characteristic glossy appearance of colonies composed of spherical cells. Genetic tests demonstrated that 25 (76%) were insertions in the rodA gene, 7 (21 %) were mre mutants, and 1 (3%) was a divD mutant. No insertion in the pbpA gene were found. Insertions in cell shape genes only appeared when strains displaying resistance to mecillinam (not caused by -lactamase production) were employed. Neither rodA nor mre insertions could be transduced to wild-type strains but they were normally accepted by mecillinam-resistant derivatives and by cya and crp mutants, which, unlike the corresponding Escherichia coli strains, did not display resistance to mecillinam. On the other hand, the divD insertion could be efficiently transduced to any strain. It is concluded that the rodA, mre, and divD genes are involved in the control of rod cell shape but, in addition, the RodA and Mre products perform some function(s) that is essential for wild-type cells but dispensable for some mecillinam-resistant strains, and for cya and crp mutants. 相似文献
107.
Seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were used in two sets of experiments in order to evaluate; (1) the reciprocal effects of each nitrogen form on net uptake of nitrate and ammonium, and (2) the effect of earlier nitrogen nutrition on ammonium versus nitrate uptake. In the former group of experiments we studied the kinetics of nitrate and ammonium uptake as well as the interference of each of the two forms with net uptake of ammonium and nitrate by both nitrogen depleted and nitrogen fed carob seedlings. On the whole, nitrogen depletion led to increase in both affinity and Vmax of the system for both forms of nitrogen, at the same time as the effects of nitrate on uptake of ammonium and vice versa were concentration dependent. In the second group of experiments the effects of earlier nitrogen nutrition on nitrate and ammonium uptake were characterized, and in this case we observed that: (a) if only one form of N was supplied, ammonium was taken up in greater amounts than nitrate; (b) the presence of ammonium enhanced nitrate uptake; (c) ammonium uptake was inhibited by nitrate; (d) there was a significant effect of the earlier nitrogen nutrition on the response of the plants to a different nitrogen source. The latter was evident mainly as regards ammonium uptake by plants grown in ammonium nitrate. The interactions between nitrate and ammonium uptake systems are discussed on the basis of the adaptation to the nitrogen source during early growth. 相似文献
108.
Plasma and liver selenium of Wistar rats were determined after 1, 3, and 6 mo supplementation with 0.5, 2, 6, or 15 ppm selenium
as sodium selenite in drinking water. Plasma selenium was not different from control values at additional intake of 0.5 ppm
but increased above usual levels at higher intakes. A highly significant correlation was observed between the total quantity
of selenium ingested and plasma selenium after 1 mo treatment (r=0.99,p<0.01), but was less pronounced after 3 and 6 mo (0.94,p<0.05, and 0.78,p<0.05, respectively). The decrease in plasma selenium with time of treatment was more pronounced at higher intakes. There
was also a highly significant correlation between total selenium intake and liver selenium concentration (r=0.99,p<0.01) after 1 mo of treatment, but this time liver selenium did not change with time, and the correlation remained highly
significant throughout the investigation. Liver selenium therefore appears as a more sensitive and more representative measure
of selenium intake than plasma selenium. Most supplements did not affect body weight and survival of animals, except when
the diet was supplemented with 15 ppm for 6 mo; however, alterations in biochemical parameters concerning lipid status and
hepatic function were observed at levels above 2.0 ppm. 相似文献
109.
Jos M Cuezva Ana I Flores Antonio Liras Juan F Santarn Agustín Alconada 《Biology of the cell / under the auspices of the European Cell Biology Organization》1993,77(1):47-62
Summary— A review of the proteinaceous machinery involved in protein sorting pathways and protein folding and assembly in mitochondria and peroxisomes is presented. After considering the various sorting pathways and targeting signals of mitochondrial and peroxisomal proteins, we make a comparative dissection of the protein factors involved in: i) the stabilization of cytosolic precursor proteins in a translocation competent conformation; ii) the membrane import apparatus of mitochondria and peroxisomes; iii) the processing of mitochondrial precursor proteins, and the eventual processing of certain peroxisomal precursor, in the interior of the organelles; and iv) the requirement of molecular chaperones for appropriate folding and assembly of imported proteins in the matrix of both organelles. Those aspects of mitochondrial biogenesis that have developed rapidly during the last few years, such as the requirement of molecular chaperones, are stressed in order to stimulate further parallel investigations aimed to understand the origin, biochemistry, molecular biology and pathology of peroxisomes. In this regard, a brief review of findings from our group and others is presented in which the role of the F1-ATPase α-subunit is pointed out as a molecular chaperone of mitochondria and chloroplasts. In addition, data are presented that could question our previous indication that the immunoreactive protein found in the rat liver peroxisomes is due to the presence of the F1-ATPase α-subunit. 相似文献
110.
The metabolism of sugar and malic acid by Leuconostoc oenos: effect of malic acid, pH and aeration conditions 总被引:1,自引:1,他引:0
M. Paula Firme M. Cristina Leitão M. Vitória San Romão 《Journal of applied microbiology》1994,76(2):173-181
The co-metabolism of sugars by Leuconostoc oenos was studied under different environmental conditions. Under aerobic conditions, growth and sugar metabolism were poorer than under CO2 or N2 atmosphere and acetic acid accumulated to a larger extent. Glycerol was found in the aerobic cultures while erythritol was detected under N2 or CO2 . When medium conditions make growth difficult (low pH, aerobic conditions, low nutrients), sugars were only slightly metabolized and growth was very slow while malic acid was rapidly and completely degraded, leading to an increase in the y ATP . Aeration effects on the malic acid degradation rate depended on the nutrients and carbon source in the medium. Malic acid clearly stimulated bacterial growth, allowing an increase in the molar growth yields and ATP production. The results suggest that under adverse conditions cells are not able to grow and malic degradation supplies additional energy production. 相似文献