全文获取类型
收费全文 | 107723篇 |
免费 | 1262篇 |
国内免费 | 895篇 |
专业分类
109880篇 |
出版年
2023年 | 111篇 |
2022年 | 199篇 |
2021年 | 418篇 |
2020年 | 319篇 |
2019年 | 341篇 |
2018年 | 12133篇 |
2017年 | 10899篇 |
2016年 | 7919篇 |
2015年 | 1412篇 |
2014年 | 1183篇 |
2013年 | 1335篇 |
2012年 | 5514篇 |
2011年 | 13865篇 |
2010年 | 12649篇 |
2009年 | 8861篇 |
2008年 | 10631篇 |
2007年 | 12140篇 |
2006年 | 1079篇 |
2005年 | 1273篇 |
2004年 | 1679篇 |
2003年 | 1655篇 |
2002年 | 1377篇 |
2001年 | 404篇 |
2000年 | 253篇 |
1999年 | 151篇 |
1998年 | 141篇 |
1997年 | 142篇 |
1996年 | 109篇 |
1995年 | 90篇 |
1994年 | 96篇 |
1993年 | 90篇 |
1992年 | 77篇 |
1991年 | 100篇 |
1990年 | 67篇 |
1989年 | 41篇 |
1988年 | 58篇 |
1987年 | 39篇 |
1986年 | 20篇 |
1985年 | 41篇 |
1984年 | 63篇 |
1983年 | 37篇 |
1982年 | 29篇 |
1981年 | 28篇 |
1980年 | 29篇 |
1978年 | 19篇 |
1977年 | 22篇 |
1975年 | 24篇 |
1972年 | 250篇 |
1971年 | 279篇 |
1962年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Achiléa Lisboa Bittencourt Maria das Graças Santana Araujo Maria do Socorro Fontoura Paes 《Mycopathologia》1980,71(3):155-158
A case of a two-year-old boy with multiple subcutaneous lesions caused by Basidiobolus haptosporus is presented.The child had also a non-toxic familial goiter and clinical and radiological features of a pulmonary illness. The pulmonary manifestations only disappeared with the treatment with potassium iodide. The authors think that the pulmonary lesions must have arisen by direct spread of the fungus from the subcutaneous lesions of the chest. 相似文献
72.
Perin L. Donnini M. Diomede L. Romano M. Tacconi M. T. Luisetti M. Salmona M. 《Cytotechnology》1991,7(1):25-32
An expression vector for G-CSF, pASLB3-3, was constructed and introduced into Namalwa KJM-1 cells (Hosoi et al., 1988), and cells resistant to 100 nM of methotrexate (MTX) were obtained. Among them, the highest producer, clone SC57, was selected and the productivity of this clone was further characterized. The maximal production of G-CSF was at the most 1.8 g/ml/day using a 25 cm2 tissue culture flask, even though the cell number was above 7×105 cells/ml. The limiting factors at high density were analyzed as the deficiency of nutrients, such as glucose, cysteine and serine, and pH control. The depression of specific G-CSF productivity per cell under the batch culture conditions was overcome by using a perfusion culture system, BiofermenterTM (Sato, 1983) with modifications of nutrients supplementation by a dialysis membrane and/or dissolved oxygen (DO) supplementation by microsilicone fibers. ITPSGF medium was modified to elevate concentrations of amino acids and glucose by 2.0- and 2.5-times, respectively. Under the control of pH at 7.4 and DO at 3 ppm, the specific G-CSF productivity was not depressed even at high cell density (above 1×107 cells/ml), and the amount of G-CSF reached 41 g/ml. These results indicated the possibility of finding the optimum culture conditions for the production of recombinant proteins by Namalwa KJM-1 cells.Abbreviations ABTS
2,2-Azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid
- BSA
Bovine Serum Albumin
- BSA-PBS
Phosphate-buffered Saline without Ca2+ and Mg2+ containing Bovine Serum Albumin
- dhfr
Dihydrofolate Reductase
- DO
Dissolved Oxygen
- G-CSF
Granulocyte Colony-stimulating Factor
- HEPES
4-(2-Hydroxyethyl)-1-piperazineethansulfonic Acid
- IFN
Interferon
- MTX
Methotrexate
- PBS(-)
Phosphate-buffered saline without Ca2+ and Mg2+
- Tween-PBS
Phosphate-buffered saline without Ca2+ and Mg2+ containing 0.05% of Tween 20 相似文献
73.
Antibodies to tubulin were prepared in rabbits by immunization with reduced-carboxymethylated calf-brain tubulin. In immunodiffusion tests the antibodies showed full cross reactivity with the immunogen as well as with native calf-brain tubulin. The same antibodies showed cross reactivity with a factor in extract of cotton (Gossypium hirsutum L.) cotyledons but there was no full immunological identity between calf-brain tubulin and this factor. A solid-phase radioimmunoassay for quantitative estimation of this plant tubulin-like factor was developed. It measured the binding of antibodies to immobilized calf-native tubulin. Competition between the unknown soluble tubulin-like factor, and immobilized tubulin was assayed at serum dilution of 1:50. Extraction conditions which preserved the antigenic properties of the tubulin-like factor from cotton cotyledons were defined. The radioimmunoassay measured quantities of the tubulin-like factor in the range of 0.1–10 g-equivalents of calf-brain tubulin. Immediately after homogenization of the tissue only 25% of the total amount of tubulin-like activity was present in soluble form, while most of it remained in the insoluble fraction. Apparent maximal solubilization was achieved spontaneously 10 h after homogenization or by treatment with guanidine hydrochloride. These results indicate that in this material, tubulin is not released immediately by homogenization but remains assembled in microtubules and-or in a bound or sequestered form.Abbreviations NRS
normal rabbit serum
- RCM
reduced-carboxymethylated 相似文献
74.
To determine the usefulness of R-wave amplitude changes during exercise testing for the diagnosis of coronary artery disease (CAD) and to understand the discrepancies that have been described in the literature regarding their value, we studied two groups of patients by means of electrocardiographic (EKG) treadmill testing and coronary arteriography. Group I was composed of 149 patients who were studied prospectively. The specificity of R-wave changes measured from preexercise to immediately postexercise (SRV(5)) was 81%, but that of R-wave changes measured from preexercise to peak exercise (URV(5)) was 46%. A group of 156 patients (Group II) evaluated retrospectively showed a high specificity for the SRV(5) (84%) and poor specificity for the URV(5) (39%). The sensitivity of the SRV(5) was 38% in Group I and 42% in Group II. Therefore, if measured during the immediate postexercise period and not at peak exercise, changes in R-wave amplitude may be of value in the diagnosis of coronary artery disease by electrocardiographic exercise testing. 相似文献
75.
Carlos M. Herrera 《Oecologia》1976,25(2):187-191
Summary An index to assess trophic diversity from presence-absence food data is proposed. The index is computed according to the expression
, where the
's are the frequencies of occurrence of the various prey categories. The upper and lower limits of D are derived. A test of the reliability of D was carried out by comparing D and H (Shannon's information function) values obtained from a set of twenty-three food analyses from vertebrate animals. Results show that, although a significant correlation exists between D and H, only a small fraction of H-variation is explained by D-variation. D contains two kinds of information, one referred to species richness and another relative to the degree of between-samples heterogeneity. The former is shared in common with H and this presumably explains the fairly weak correlation found between both measures. 相似文献
76.
77.
78.
Carlos A. Leguizamón 《Bulletin of mathematical biology》1975,37(6):675-689
A theory for environmental systems is defined on the basis of two elements, termed ‘environmental unity’ and ‘behavior’. Environmental systems are regarded as non-living systems, each one related with only one biological system. We construct a material-energetic environmental diagram, which is introduced in terms of the theory of categories, thereby giving rise to a new categoryE. By means of two biological conditions, and the definition of static property of the biological system (related to its own environment), a set of theorems is obtained, exhibiting mathematical consequences for the represented theory. 相似文献
79.
Guno Haskå 《Microbial ecology》1975,1(1):234-245
Myxobacteria presumably produce extracellular bacteriolytic enzymes when they are growing in soil. In order to study their ecological significance, adsorption experiments were performed with lytic enzymes produced byMyxococcus virescens in casitone media. Different soils as well as montmorillonite and kaolinite can rapidly adsorb the bacteriolytic but not the proteolytic enzymes. About 1 gm of montmorillonite per liter of cell-free culture solution is enough for the adsorption of 97% of the bacteriolytic enzymes. The adsorption per unit weight is about 100 times greater on montmorillonite than on kaolinite. About 40% of the adsorbed enzymes can be eluted with solutions of high pH or high ionic strength. The only desorbed bacteriolytic enzyme is the alanyl-∈-N-lysine endopeptidase. 相似文献
80.