全文获取类型
收费全文 | 926篇 |
免费 | 64篇 |
出版年
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 32篇 |
2014年 | 27篇 |
2013年 | 47篇 |
2012年 | 46篇 |
2011年 | 38篇 |
2010年 | 29篇 |
2009年 | 15篇 |
2008年 | 47篇 |
2007年 | 45篇 |
2006年 | 39篇 |
2005年 | 54篇 |
2004年 | 47篇 |
2003年 | 55篇 |
2002年 | 54篇 |
2001年 | 32篇 |
2000年 | 31篇 |
1999年 | 25篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1967年 | 6篇 |
排序方式: 共有990条查询结果,搜索用时 250 毫秒
31.
Effects on positive phototaxis and the cell motility of 7 cationsin 5mM MOPS (morpholinopropane sulfonic acid) buffer (pH 7.0)containing 0.16 mM NaCl, 0.68 mM KCl, 0.5 mM CaCl2 and 0.16mM MgCl2 were studied in the unicellular flagellate Cryptomonaswith a photoelectrical measuring apparatus and photomicrography.When calcium ion was removed from the medium by adding 1 mMEGTA (ethylene glycol-bis-(ß-amino-ethylether)-N,N'-tetraaceticacid), the phototactic response was totally inhibited, but theswimming rate was not much affected. The effect of EGTA waspartially reversed by the addition of 1 mM CaCl2. When 15mMKCl or RbCl was added to the medium, phototaxis was greatlyinhibited, but there was no significant influence on the swimmingrate. Similar but less inhibitory effects were induced in thepresence of NaCl, LiCl and CsCl. KCl-induced inhibition waspartially removed by the addition of 15 mM CaCl2 or MgCl2. (Received June 25, 1982; Accepted September 27, 1982) 相似文献
32.
33.
The performance of a cytology laboratory can be objectively quantitated as the total discrimination, a defined quantity of information. The total discrimination is dependent on the number of categories used in gynecologic cytology and on the corresponding histologic states; over-classification results in a higher rate of misinformation and reduced total discrimination. Total divergence is another measure of the association between cytologic categories and histologic states; in contrast to the total discrimination, the total divergence does not require a one-to-one correspondence between the cytologic categories and the histologic states. Using data from the Gynecologic Cytology Laboratory of the University of Minnesota, the total discrimination was maximized when gynecologic cytology used three categories of diagnosis, consisting of (1) normal, atypical benign or reactive atypia, (2) cervical intraepithelial neoplasia (CIN) and (3) all malignancies. The use of four categories, (1) normal, atypical benign or reactive atypia, (2) mild or moderate dysplasia, (3) severe dysplasia or squamous carcinoma in situ and (4) all malignancies, was almost equally informative. Observations on the total divergences resulted in similar conclusions. These findings generally support the recommendation of the consensus workshop sponsored by the National Cancer Institute (the Bethesda System nomenclature) to group all degrees of CIN into two large categories. 相似文献
34.
Mechanisms of somatic embryogenesis in cell cultures: Physiology,biochemistry, and molecular biology
A. Komamine R. Kawahara M. Matsumoto S. Sunabori T. Toya A. Fujiwara M. Tsukahara J. Smith M. Ito H. Fukuda K. Nomura T. Fujimura 《In vitro cellular & developmental biology. Plant》1992,28(1):11-14
Summary One of the most characteristic cell functions in plants is totipotency. Somatic embryogenesis can be regarded as a model system
for the investigation of mechanisms of totipotency, because a high frequency and synchronous embryogenic system from single
somatic cells has been established in carrot suspension cultures. Four phases are recognized in this process, and several
molecular markers, viz. polypeptides, mRNAs, antigens against monoclonal antibodies, can be detected during the expression
of totipotency, but they disappear during its loss. Four organ-specific genes have been isolated from hypocotyls and roots
by differential screening. They were expressed preferentially after the globular-heart stages of embryogenesis, and were strongly
suppressed by auxin. A CEM 1 gene was isolated by differential screening of embryogenic cell clusters. This gene was expressed
strongly and transiently during the proglobular and globular stages. The sequence of CEM 1 was found to encode a polypeptide
showing high homology to the elongation factor isolated from eucaryotic cells. Thus good progress is being made in understanding
the basic mechanisms of somatic embryogenesis.
Presented in the Session-in-Depth Developmental Biology of Embryogenesis at the 1991 World Congress on Cell and Tissue Culture,
Anaheim, California, June 16–20, 1991. 相似文献
35.
Inflammatory pseudotumor of the lung diagnosed as granulomatous lesion by preoperative brushing cytology. A case report 总被引:1,自引:0,他引:1
The clinical and cytologic features of a case of inflammatory pseudotumor of the lung are presented. Chest roentgenograms revealed a solitary circumscribed round mass in a nine-year-old boy. The mass was diagnosed as a granulomatous lesion by bronchoscopic brushing cytology. Although smears and cultures of sputum and brushing specimens were negative for tuberculosis, a tuberculin reaction was positive and antitubercular therapy was instituted. Since the mass had grown further after six months of therapy, an open lung biopsy was performed to resect the lesion and establish the diagnosis. Imprint smears of the cut surface of the lesion showed cytologic features similar to those of the brushings: short, spindle-shaped cells with a tendency to be arranged in stori-form patterns against a background of minimal necrotic debris. Histopathology established the final diagnosis of inflammatory pseudotumor, a rare granulomatous lesion radiologically resembling a true tumor. Since this lesion usually occurs in younger patients, inflammatory pseudotumor should be considered in pediatric cases with an intrapulmonary lesion that shows histiocytic spindle-shaped cells in stori-form patterns, but whose smears and cultures test negative for tuberculosis. 相似文献
36.
Kenji Fukuzawa Hisako Chida Akira Tokumura Hiroaki Tsukatani 《Archives of biochemistry and biophysics》1981,206(1):173-180
The antioxidative effect of α-tocopherol incorporated into lecithin liposomes was studied. Lipid peroxidation of liposome membranes, assayed as malondialdehyde production, was catalyzed by ascorbic acid and Fe2+. The peroxidation reaction, which did not involve the formation of singlet oxygen, superoxide, hydrogen peroxide, or a hydroxyl radical, was inhibited by α-tocopherol and a model compound of α-tocopherol, 2,2,5,7,8-pentamethyl-6-hydroxy-chroman (TMC), but not by phytol, α-tocopherylquinone, or α-tocopheryl acetate. One mole of α-tocopherol completely prevented peroxidation of about 100 moles of polyunsaturated fatty acid. Decrease in membrane fluidity by lipid peroxidation, estimated as increase of fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) embedded in the membrane, was also inhibited by α-tocopherol and TMC, reflecting their antioxidant functions. Cholesterol did not act as an antioxidant, even when incorporated in large amount into the liposome membranes, but it increased the antioxidative efficiency of α-tocopherol. When a mixture of liposomes with and without α-tocopherol was incubated with Fe2+ and ascorbic acid, α-tocopherol did not protect the liposomes not containing α-tocopherol from peroxidation. However, preincubation of the mixture, or addition of Triton X-100 allowed the α-tocopherol to prevent peroxidation of the liposomes not containing α-tocopherol. In contrast, in similar experiments, liposomes containing TMC prevented peroxidation of those without TMC without preincubation. Tocopherol in an amount so small as to exhibit only a slight antioxidative effect was oxidized when incorporated in egg lecithin liposomes, but it mostly remained unoxidized when incorporated in dipalmitoyllecithin liposomes, indicating that oxygen activated by ascorbic acid-Fe2+ does not oxidize α-tocopherol directly. Thus, decomposition of α-tocopherol may be caused by its interaction with peroxy and/or alkoxyl radicals generated in the process of lipid peroxidation catalyzed by Fe2+ and ascorbic acid. 相似文献
37.
Jonathan Rosen Thomas Ryder Hachiro Inokuchi Hisako Ohtsubo Eiichi Ohtsubo 《Molecular & general genetics : MGG》1980,179(3):527-537
Summary The nucleotide sequence of the entire region required for autonomous replication and incompatibility of an R100 plasmid derivative, pSM1, has been determined. This region includes the replication region and all plasmid encoded information required for replication. Numerous reading frames for possible proteins can be found in this region. The existence of one of these proteins called RepA1 (285 amino acids; 33,000 daltons) which is encoded within the region known by cloning analysis to be required for replication is supported by several lines of evidence. These include an examination of the characteristic sequences on the proximal and distal ends of the coding region, a comparison of the sequence of the replication regions of pSM1 and the highly related R1 plasmid derivative Rsc13 as well as other biochemical and genetic evidence. The existence of two other proteins, RepA3 (64 amino acids; 7000 daltons) and RepA2 (103 amino acids; 11,400 daltons) is also consistent with most of the criteria mentioned above. However, the region encoding RepA3, which by cloning analysis is within the region responsible for both replication and incompatibility, has never been demonstrated to produce a 7,000 dalton polypeptide. Since a large secondary structure can be constructed in this region, it is possible that the region contains structure or other information that is responsible for incompatibility. RepA2, encoded entirely within the region identified by cloning analysis to be responsible for incompatibility but not for replication can be visualized in vivo and in vitro. However, the nucleotide sequence of the region encoding RepA2 is completely different in mutually incompatible plasmid derivatives of R1 and R100. It is therefore unlikely that RepA2 plays a major role in incompatibility. Thus, we predict that RepA1 is required to initiate DNA synthesis at the replication origin and that the region proximal to RepA1 either encodes a gene product or structure information that is responsible for incompatibility. 相似文献
38.
Takashi Muramatsu Hisako Muramatsu Masataka Kasai Sonoko Habu Ko Okumura 《Biochemical and biophysical research communications》1980,96(4):1547-1553
agglutinin (DBA), which is specific for terminal α-N-acetylgalactosamine, bound to a spontaneous leukemia cell of mice, but not to lymphoid cells of the host. The DBA receptors were isolated from the leukemia cell labeled with [3H]-galactose after detergent solubilization and affinity chromatography on DBA-agarose. The major component of the receptors migrated as a glycoprotein of apparent molecular weight 100,000 upon SDS gel electrophoresis. Alkaline treatment degraded the glycoproteins, releasing oligosaccharides of molecular weight around 1,000. 相似文献
39.
Leila J. Walker M.S. Joseph W. Landau M.D. Hisako Nishihara Sc.D. Victor D. Newcomer M.D. 《Mycopathologia》1965,27(3-4):301-304
Summary The level of haptoglobin was determined in control rats and in rats infected withC. immitis. The haptoglobin levels in the infected group were significantly higher than in those in the control group. The possibility that serial determinations may be of value in following the course of this disease is currently being investigated.This study was supported in part by USPHS Grants A1-06048-01, 5 T1 A1 52–06 and the Dermatologic Research Foundation of California, Inc. 相似文献
40.
Joan H. Fujimura 《New genetics and society》2013,32(2):195-226
Abstract This article discusses the production of new “postgenomic” knowledges that aim to be more ecological and “wholistic” than the reductionist genetics of the last forty years. It examines systems biology and, briefly, developmental systems theory, which are two approaches that attempt to model complexities in biology. System biological metaphors and languages have been in part taken from engineering models of automobiles, airplanes and robots and then applied to complex living systems. Systems biology is only the most recent example and perhaps an excellent case in which to study this movement back and forth across the machine-living organism border in Euro-American biology to track how what we know to be nature and machine is constituted. This article argues for a careful analysis of this historical production specifically around the question of what is lost in translation at these border crossings and their potential consequences. 相似文献