全文获取类型
收费全文 | 5202篇 |
免费 | 479篇 |
国内免费 | 6篇 |
专业分类
5687篇 |
出版年
2023年 | 32篇 |
2022年 | 50篇 |
2021年 | 119篇 |
2020年 | 65篇 |
2019年 | 86篇 |
2018年 | 85篇 |
2017年 | 64篇 |
2016年 | 144篇 |
2015年 | 215篇 |
2014年 | 254篇 |
2013年 | 296篇 |
2012年 | 438篇 |
2011年 | 404篇 |
2010年 | 262篇 |
2009年 | 260篇 |
2008年 | 347篇 |
2007年 | 350篇 |
2006年 | 285篇 |
2005年 | 267篇 |
2004年 | 258篇 |
2003年 | 230篇 |
2002年 | 223篇 |
2001年 | 47篇 |
2000年 | 25篇 |
1999年 | 33篇 |
1998年 | 67篇 |
1997年 | 37篇 |
1996年 | 31篇 |
1995年 | 34篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 30篇 |
1981年 | 30篇 |
1980年 | 39篇 |
1979年 | 19篇 |
1978年 | 29篇 |
1977年 | 23篇 |
1976年 | 22篇 |
1974年 | 24篇 |
1973年 | 17篇 |
排序方式: 共有5687条查询结果,搜索用时 0 毫秒
31.
32.
Direct Measurement of Potential Difference across the Human Red Blood Cell Membrane 总被引:2,自引:0,他引:2 下载免费PDF全文
The electrical potential difference across the human red cell membrane has been measured directly. A biological amplifier with neutralized input capacity was used. Human red cells in modified Ringer solution were impaled individually with 3 M KCl-filled glass microelectrodes. Movements of the microelectrodes were effected by Leitz micromanipulators. Results showed a potential difference of -8.0 ± 0.21 (SEM) mv, the inside being negative with respect to the outside. This value is approximately that calculated by using the Nernst equation considering the intracellular and extracellular chloride concentrations.
As a control, similar measurements were made on nylon microcapsules containing hemoglobin. The measured potential of -0.52 ± 0.02 (SEM) mv, which agreed very well with the value calculated on the basis of Donnan equilibrium, was much smaller in magnitude as compared to the results for the red cell, and there was evidence of fixed charges on the microcapsule membrane. There was no evidence of this in the case of the red cell.
相似文献33.
We have observed pigmented cytoplasmic granules, with the characteristic staining properties of lipofuscin (ceroid, "wear-and-tear") pigment, in newborn human liver. The pigment is found at the periphery of the lobule in hepatocytes and some bile ductular cells. It is acid-fast, PAS-positive after diastase digestion, slightly argyophilic and sudanophilic, and markedly Schmorl's- and peroxidase positive in paraffin sections. Difficult to see in sections stained with hematoxylin and eosin, the pigment can be detected in unstained sections. The granules also resemble lipofuscin found in adult tissues, in their ultra-structural and enzymatic properties. They are polymorphic, contain granular material of moderate and high electron opacity, and are delimited by a single membrane. Acid phosphatase and β-glucuronidase activities are visualized in the newborn granules, identifying them as lysosomes. The granules also contain copper and, to a much lesser extent, iron. The accumulation of lipofuscin pigment in lysosomes in many tissues correlates well with aging, and this process has been interpreted as a reflection of cellular degeneration or wear-and-tear. However, the presence of lipofuscin granules as a constant component of neonatal liver suggests that they are not a measure of cellular senescence. 相似文献
34.
The amino sugar content of spoiling beef increased with the microbial count and appeared to be responsible for the increased hydration capacity of spoiled meats. 相似文献
35.
36.
37.
38.
A FERROUS-ION-OXIDIZING BACTERIUM I. : Isolation and Some General Physiological Characteristics 总被引:6,自引:3,他引:3 下载免费PDF全文
Jay V. Beck 《Journal of bacteriology》1960,79(4):502-509
39.
Evaluation of the Extract-Release Volume Phenomenon as a Rapid Test for Detecting Spoilage in Beef 总被引:1,自引:0,他引:1 下载免费PDF全文
Ground beef of several grades, obtained fresh and held refrigerated until spoiled, was presented to a test panel for scoring on color, odor, and tactile response (tackiness) as to degree of acceptance. Panel scores were correlated with total bacterial counts, ninhydrin-reactive substances, and ERV (extract-release volume) on the same meat. ERV correlated highest with bacterial counts the largest number of times; tackiness, odor, ninhydrin, and color followed in that order. Correlation between bacterial numbers and organoleptic qualities was best, with tackiness followed closely by odor, and then by color. Correlation between tackiness and odor was high. The degree of correlation between bacterial numbers, tackiness, and ERV was high enough to warrant the use of the ERV phenomenon as a rapid test of microbial quality of beef. An ERV value of 25 under the conditions of the test was supported as a divider between acceptable and unacceptable ground beef. 相似文献
40.
A selective herbicide IPC (o-isopropyl-N-phenlycarbamate) causes contraction of chromosomes in the prophase, metaphase, and anaphase stages of mitosis in cells of treated root tips. Effective concentrations in aqueous solution lie between 2.5 and 50 ppm, and effective times between 1 and 4 hr, depending upon the species of plant. A suggested starting combination is 10 ppm for 2 hr. This compound is effective in causing contraction of chromosomes in a wide range of plant species, as well as enhancing separation in acetocarmine and aceto-orcein squashes in many cases. Possibly, it may produce similar results in species which have been found to be unaffected by colchicine, 8-hydroxyquinoline, p-dichlorobenzene, and other commonly used chemicals. 相似文献