全文获取类型
收费全文 | 2294篇 |
免费 | 108篇 |
国内免费 | 1篇 |
出版年
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 23篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 32篇 |
2015年 | 56篇 |
2014年 | 104篇 |
2013年 | 174篇 |
2012年 | 129篇 |
2011年 | 138篇 |
2010年 | 97篇 |
2009年 | 74篇 |
2008年 | 117篇 |
2007年 | 164篇 |
2006年 | 149篇 |
2005年 | 132篇 |
2004年 | 177篇 |
2003年 | 139篇 |
2002年 | 164篇 |
2001年 | 28篇 |
2000年 | 36篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 28篇 |
1993年 | 27篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有2403条查询结果,搜索用时 15 毫秒
1.
A low-pressure microwave-induced helium plasma serves as an excitation source for metal chlorides, nitrates, and sulfates vaporized from a filament, resulting in fractional vaporization and differential sensitivities of detection of the elements depending on the vapor pressures of their salts. The shapes of the single emission peaks, which are simple in the presence of potassium chloride, become complex and may double in number. 相似文献
2.
3.
Molecular oxygen controls nitrate transport of Escherichia coli nitrate-respiring cells 总被引:4,自引:0,他引:4
Escherichia coli cells grown anaerobically in the presence of nitrate reduce the nitrate as a terminal electron acceptor in place of molecular oxygen by an induced respiratory-type electron transferring system residing in the inner membrane structure. When oxygen is introduced to a suspension of nitrate-respiring cells, the oxygen is immediately reduced preferentially and the cellular uptake of nitrate ceases abruptly. In contrast, we found that the cells exhibited no oxygen control on uptake of chlorate, a competitive substrate analogue, indicating operation of an oxygen-sensitive transport system specific to nitrate. This was further evidenced by the fact that chlorate inhibition of reduction of nitrate was brought about only when the transport of both chlorate and nitrate was facilitated by the aid of carrier-type chlorate (or nitrate) ionophore. We demonstrated that oxygen inhibition on reduction of nitrate was abolished within the cells treated by octyl glucoside resulting in a removal of permeability barrier specific to nitrate. We conclude that the transient control by molecular oxygen is primarily due to the inhibition of nitrate transport into the cytoplasmic side. Since nitrate induces the nitrate-respiring system, the repression of the nitrate reductase operon by molecular oxygen is consistently interpreted on the basis of the "inducer exclusion mechanism." 相似文献
4.
Spin label study of erythrocyte deformability. Ca2+-induced loss of deformability and the effects of stomatocytogenic reagents on the deformability loss in human erythrocytes in shear flow 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The Ca2+-induced loss of deformability in human erythrocytes and the recovery of the lost deformability by stomatocytogenic reagents were investigated by means of a new flow electron paramagnetic resonance (EPR) spin label method, which provides information on deformation and orientation characteristics of spin labeled erythrocytes in shear flow. The Ca2+-induced loss of deformability is attributed mainly to the increase in intracellular viscosity resulting from efflux of intracellular potassium ions and water (Gardos effect). Partial recovery of the lost deformability is demonstrated in the presence of stomatocytogenic reagents, such as chlorpromazine, trifluoperazine, W-7, and calmidazolium (R24571). The recovery can not be explained solely by suppression of the Gardos effect due to the reagents. Incorporation of an optimal amount of the reagents into the membrane appears to compensate for the membrane modification due to Ca2+ ions to restore a part of the lost deformability. 相似文献
5.
Junichi Ishihara Nagahiro Saijo Yasutsuna Sasaki Hidehiko Nakano Akira Ozaki Hidenobu Takahashi Masanori Sakurai Kazuhiko Nakagawa Masaaki Iigo Fumihiko Kanzawa Akio Hoshi Weon Seon Hong James R. Jett Terumi Takahashi 《Cancer immunology, immunotherapy : CII》1987,24(3):185-189
Summary The antitumor effect of recombinant human tumor necrosis factor (rH-TNF) on two clones of rat fibrosarcoma with different metastatic potential to lymph nodes was examined. The colony formation of clone A, which has high metastatic potential, was completely inhibited by continuous exposure to rH-TNF at 50 U/ml. In contrast, colony formation of clone G, which has low metastatic potential, was not inhibited by high concentrations of rH-TNF (10,000 U/ml). The inhibitory effect of rH-TNF on colony formation by clone A was also observed with a 1-h exposure to rH-TNF. This effect was time and concentration dependent, as determined by the colony assay, 3H-thymidine uptake assay, and 51Cr-release assay. 3H-thymidine and 3H-uridine uptake per cell of clone A exposed to rH-TNF was not decreased. This suggests that the mechanisms of the antitumor effect of rH-TNF were not due to inhibition of DNA and RNA synthesis of tumor cells. In vivo growth and lymph node metastases of clone A inoculated i.p. to Donryu strain rats were completely suppressed by 14 consecutive i.p. injections of 105 or 106 U/kg per day of rH-TNF. On the other hand the growth of clone G was not influenced by rH-TNF administration. 相似文献
6.
Yasuhiko Asada Yoshio Kimura Masaaki Kuwahara Akira Tsukamoto Kazuo Koide Atsuhiro Oka Mitsuru Takanami 《Applied microbiology and biotechnology》1988,29(5):469-473
Summary A ligninase gene has been cloned from a Phanerochaete chrysosporium genomic DNA library. Nucleotide sequencing of the gene has revealed that the ligninase structural gene contains 1116 bp of the protein-encoding sequence, of which 84 bp encode the signal peptide. The protein-encoding sequence is interrupted by eight introns which conform to the universal G-T/A-G splicing rule observed for the 3 and 5 intron boundaries. The putative eukaryotic regulatory sequences, i.e. CAAT and TATA box-like sequences, are present in the 5 flanking region. 相似文献
7.
Masaaki Takeshita Seiji Nakamura Fujio Makita Susumu Ohwada Yukio Miyamoto Yasuo Morishita 《Biotherapy》1992,4(2):139-145
We examined whether orally administered RBS (rice bran saccharide), prepared from rice bran by hot water extraction, increases immunocompetence, inhibits gastrointestinal carcinogenesis with N-ethyl-N-nitro-N-nitrosoguanidine (ENNG) or shows an antitumor effect. After the administration of RBS, phytohemagglutinin (PHA)- and pokeweed mitogen (PWM)-stimulated blastogenesis of lymphocytes derived from the mesenteric lymph nodes and peripheral blood was enhanced, and the helper/ suppressor T-cell ratio was elevated, and migration activity of peritoneal macrophages was also increased in rats treated continuously with ENNG. ENNG-induced gastrointestinal carcinomas were observed in 43% of those administered RBS (ENNG-RBS) as compared with 88% in the control (ENNG) and 94% in the prednisolone (PRD) group (ENNG-PRD). The 12-month survival rate of rats bearing gastrointestinal cancer was 58% in the ENNG-RBS group as compared with 25% in the ENNG group and 15% in the ENNG-PRD group. RBS prevented the reduction in immunocompetence in the course of carcinogenesis, suppressed carcinogenesis, and prolonged the survival of rats with gastrointestinal cancer. Antitumor activities of RBS are thought to be a kind of host mediated action. The growth inhibition ratio of transplantable ENNG-induced cancer in Wistar rats was 42.1% in the RBS and 51.8% in the 5-FU group. Since little is known about the potent antitumor activity of -glucan, it would be interesting to consider the relationship between the structure and the biological activities of polysaccharides. 相似文献
8.
Summary We have developed a bioreactor system for aerobic fermentation, using a new ceramic carrier APHROCELL which has a suitable shape for liquid and gas passage. In acetic acid fermentation byAcetobacter cells from ethanol, as a typical example of aerobic fermentation, a productivity of 17.25 g/l h was attained at continuous production of 23 g-acetic acid/l; at an acetic acid concentration around 53 g/l, the productivity was 6.4 g/l h. Thus a marketable vinegar can be obtained continuously by this bioreactor system. Because of the simplicity of the APHROCELL reactor, scale up should be relatively easy. 相似文献
9.
Masahiko Sakaguchi Kazumitsu Hanai Kunimasa Ohta Masaaki Kitajima Sachiko Matsuhashi Katsuji Hori Hiromichi Morita 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1991,168(4):409-416
Summary Reduced glutathione evokes a feeding response, the tentacle-ball formation inHydra japonica. This response consists of at least 5 components (R1–R5). We raised 6 monoclonal antibodies (mAbs), each of which depressed a specific subset of these components, and we also examined the immunocytochemical localization of antigens with these mAbs at light microscopic level. The 2 mAbs that depressed R2 and R4 bound to the cnidocils of the desmoneme and the stenotele nematocytes; the 3 mAbs that depressed R5 bound to the apical surface adjacent to the cnidocils of the nematocytes; and the 2 mAbs that depressed R1 and R3 bound to the apical spot structures of unidentified cells in the ectoderm.Together with the specificity of the action of the mAbs on the behavioral response, the correspondence between the effects on the response and the structures visualized with these mAbs suggests that these structures include components of the receptor-effector system relevant to chemoreception. 相似文献
10.
Atsushi Ikai Masaaki Nishigai Toshiya Osada Hideo Arakawa Masako Kikuchi 《The protein journal》1987,6(1):81-93
The plasma α2-macroglobulin and its egg white homologue ovomacroglobulin were purified from several different species and their structure before and after the reaction with proteinases studied by electron microscopy. The negatively stained specimens showed either a ringlike structure or a flowerlike one before the reaction with proteinses, but their structures changed into open rectangular ones after the reaction. The translational frictional ratio f/f 0 of human α2-macroglobulin and crocodilian ovomacroglobulin given in the literature is between 1.5 and 1.6 before and after the reaction with proteinases. The value reflects asymmetry due not to a high axial ratio, but rather to an openness of the structure resulting in a partially free draining character of the molecules. The computational method developed by Bloomfield and his co-workers based on the formalism of Kirkwood is used to calculate the frictional ratio of several models constructed from small spheres. The overall shape of the models is derived from electron micrographs. Although the degree of hydration is an unknown parameter in the calculation, reasonable agreement is obtained between the experimental values of f/f 0 and the calculated ones. Combination of electron microscopic and hydrodynamic methods would be fruitful in the structural study of giant proteins such as α2-macroglobulin. 相似文献