全文获取类型
收费全文 | 7283篇 |
免费 | 369篇 |
国内免费 | 8篇 |
专业分类
7660篇 |
出版年
2023年 | 14篇 |
2022年 | 33篇 |
2021年 | 71篇 |
2020年 | 43篇 |
2019年 | 67篇 |
2018年 | 98篇 |
2017年 | 86篇 |
2016年 | 119篇 |
2015年 | 199篇 |
2014年 | 254篇 |
2013年 | 523篇 |
2012年 | 428篇 |
2011年 | 444篇 |
2010年 | 282篇 |
2009年 | 287篇 |
2008年 | 470篇 |
2007年 | 476篇 |
2006年 | 446篇 |
2005年 | 510篇 |
2004年 | 492篇 |
2003年 | 460篇 |
2002年 | 424篇 |
2001年 | 78篇 |
2000年 | 71篇 |
1999年 | 70篇 |
1998年 | 102篇 |
1997年 | 77篇 |
1996年 | 86篇 |
1995年 | 84篇 |
1994年 | 59篇 |
1993年 | 65篇 |
1992年 | 66篇 |
1991年 | 56篇 |
1990年 | 51篇 |
1989年 | 44篇 |
1988年 | 38篇 |
1987年 | 49篇 |
1986年 | 34篇 |
1985年 | 35篇 |
1984年 | 46篇 |
1983年 | 33篇 |
1982年 | 42篇 |
1981年 | 35篇 |
1980年 | 24篇 |
1979年 | 34篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1973年 | 14篇 |
1970年 | 11篇 |
排序方式: 共有7660条查询结果,搜索用时 15 毫秒
41.
Serratia marcescens mutants, which excrete Escherichia coli alkaline phosphatase (APase) encoded by the plasmid-bearing phoA gene, were isolated after mutagenesis by N-methyl--nitro-N-nitrosoguanidine. These mutants produced two to four times as much APase as did the parent strain under a phosphate-limiting condition, and more than 70% of the enzyme was released into the culture medium. In addition, overproduction and excretion of beta-lactamase was observed in these mutants. 相似文献
42.
Effects of an antisense napin gene on seed storage compounds in transgenic Brassica napus seeds 总被引:4,自引:0,他引:4
Junko Kohno-Murase Makoto Murase Hiroaki Ichikawa Jun Imamura 《Plant molecular biology》1994,26(4):1115-1124
To manipulate the quantity and quality of storage components in Brassica napus seeds, we have constructed an antisense gene for the storage protein napin. The antisense gene was driven by the 5-flanking region of the B. napus napin gene to express antisense RNA in a seed-specific manner. Seeds of transgenic plants with antisense genes often contained reduced amounts of napin. In some transgenic plants, no accumulation of napin was observed. However, the total protein content of transgenic and wild-type seeds did not differ significantly. Seeds lacking napin accumulated 1.4 to 1.5 times more cruciferin than untransformed seeds, although the oleosin content was not affected. Fatty acid content and composition in the seeds of transgenic plants were also analyzed by gas chromatography. Though the total fatty acid content of the transformants was the same as that of non-transformants, there was a reduction in 18:1 contents and a concomitant increase of 18:2 in seeds with reduced napin levels. This observed change in fatty acid composition was inherited in the next generation. 相似文献
43.
Summary A rapid, simple, and sensitive method for plasmid copy number comparison was developed. The extracted plasmids from the same
amount of cells were subjected to agarose gel electrophoresis and the gels photographed. The photographs were processed by
a Macintosh image analyser to enumerate the densities of plasmid bands. As a size reference, λ-DNA digested with a restriction
enzyme was used. The densities divided by size of plasmids (base pair) would represent relative values of their copy numbers. 相似文献
44.
Yasuyuki Takeda Makoto Tanaka Hiroyuki Miyazaki Suguru Takeo Kikuo Nomoto Yasunobu Yoshikai 《Cancer immunology, immunotherapy : CII》1994,38(3):143-148
The growth of MethA tumor was significantly inhibited by oral administration of the -glucan SPR-901 in BALB/c (+/+) mice but not in nude mice. Mice treated orally with SPR-901 exhibited an augmentation of antigen-specific resistance against rechallenge with the tumor cells. The tumor-neutralizing activity of regional lymph node cells from MethA-bearing mice against the tumor was augmented by oral administration of SPR-901. The tumor-neutralizing activity of lymph node cells from SPR-901-treated mice mainly appeared in Lyt2+cells. Furthermore, lymphokine-activated killer activity of these cells was enhanced by administration of SPR-901. The antitumor effect of SPR-901 was abrogated in mice depleted of either L3T4+ or Lyt2+ cells, and in cyclosporin-A-treated mice. These results suggest that Lyt2+ cells are important effector cells in MethA-bearing mice orally adminstered SPR-901 and that functional exertion of both Lyt2+ and L3T4+T cells is necessary for the antitumor effect of orally administered SPR-901 in vivo. 相似文献
45.
Sakamoto Atsushi; Ohsuga Hiroyuki; Wakaura Makoto; Mitsukawa Norihiro; Hibino Takashi; Masumura Takehiro; Sasaki Yukiko; Tanaka Kunisuke 《Plant & cell physiology》1993,34(6):965-968
A cDNA clone for copper/zinc-superoxide dismutase (Cu/Zn-SOD)was isolated from spinach (Spinacia oleracea L.) leaves. Itsnucleotide sequence showed that it codes for a precursor polypeptideof 222 amino acids, including the NH2-terminal 68-residue extensionwhich corresponds to a plastidic transit peptide. Northern hybridization,using plastidic and cytosolic Cu/Zn-SOD cDNAs as the probes,revealed that these two genes are differentially expressed inthe roots and leaves of spinach.
1Present address: Department of Biochemistry and Microbiology,Cook College, Rutgers University New Brunswick, NJ 08903-0231,U.S.A. 相似文献
46.
Abstract The blood cells of a solitary ascidian, Halocynthia roretzi, were examined by electron microscopy (EM) with reference to their appearance by light microscopy (LM). In addition, their movement and stainability by vital dyes was observed by phase-contrast microscopy, and their stainability by Giemsa was also examined. Nine cell types were recognized: vacuolated cells, hyaline amoebocytes, small amoebocytes, granular amoebocytes, macrogranular cells, globular cells, lymphocyte-like cells, large basophilic cells and large granular cells. Vacuolated cells were found to possess various numbers of vacuoles containing strongly electron-dense materials and could be divided into at least three subgroups. Granular amoebocytes contained microfilaments and many granules of uniform size. Hyaline amoebocytes and small amoebocytes seemed to be specialized as phagocytes. Macrogranular cells and globular cells were not well characterized. In the blood of adult individuals, hemoblasts were rarely found, although lymphocyte-like cells were present. Each of two large cells, large basophilic cells and large granular cells, possessed novel granules or vacuoles, whose functions remain to be elucidated. The possible functions and relationships of these cells among various ascidian species are discussed. 相似文献
47.
The behavior of cell nuclei, mitochondrial nucleoids (mt-nucleoids) and plastid nucleoids (ptnucleoids) was studied in the
root apical meristem of Arabidopsis thaliana. Samples were embedded in Technovit 7100 resin, cut into thin sections and stained with 4′-6-diamidino-2-phenylindole for
light-microscopic autoradiography and microphotometry. Synthesis of cell nuclear DNA and cell division were both active in
the root apical meristem between 0 μm and 300 μm from the central cells. It is estimated that the cells generated in the lower
part of the root apical meristem enter the elongation zone after at least four divisions. Throughout the entire meristematic
zone, individual cells had mitochondria which contained 1–5 mt-nucleoids. The number of mitochondria increased gradually from
65 to 200 in the meristem of the central cylinder. Therefore, throughout the meristem, individual mitochondria divided either
once or twice per mitotic cycle. By contrast, based on the incorporation of [3H]thymidine into organelle nucleoids, syntheses of mitochondrial DNA (mtDNA) and plastid DNA (ptDNA) occurred independently
of the mitotic cycle and mainly in a restricted region (i.e., the lower part of the root apical meristem). Fluorimetry, using
a videointensified microscope photon-counting system, revealed that the amount of mtDNA per mt-nucleoid in the cells in the
lower part of the meristem, where mtDNA synthesis was active, corresponded to more than 1 Mbp. By contrast, in the meristematic
cells just below the elongation zone of the root tip, the amount of mtDNA per mt-nucleoid fell to approximately 170 kbp. These
findings strongly indicate that the amount of mtDNA per mitochondrion, which has been synthesized in the lower part of the
meristem, is gradually reduced as a result of continual mitochondrial divisions during low levels of mtDNA synthesis. This
phenomenon would explain why differentiated cells in the elongation zone have mitochondria that contain only extremely small
amounts of mtDNA.
This work was supported by a Grant-in Aid (T.K.) for Special Research on Priority Areas (Project No. 02242102, Cellular and
Molecular Basis for Reproduction Processes in Plants) from the Ministry of Education, Science and Culture of Japan and by
a Grant-in Aid (T.K.) for Original and Creative Research Project on Biotechnology from the Research Council, Ministry of Agriculture,
Forestry and Fisheries of Japan. 相似文献
48.
Nobuakira Takeda Akira Tanamura Takaaki Iwai Mitsutoshi Kato Kenji Noma Makoto Nagano 《Molecular and cellular biochemistry》1993,129(2):139-143
The effects of captopril, an angiotensin-converting enzyme inhibitor, on congestive heart failure (CHF) were investigated in animal and clinical studies. Congestive heart failure was induced in rats by a combination of pressure and volume overload. Cardiac pressure overload was induced by constricting one renal artery (Goldblatt rat) and volume overload was induced by aorto-caval fistula. Captopril (100 mg/kg/day) was then administered for 14 weeks. Isometric contraction was assessed using isolated left ventricular papillary muscles. The maximum developed tension and the maximum rate of increase in tension (dT/dtmax) were decreased in untreated rats with CHF and improved in captopriltreated rats. The left ventricular myosin isoenzyme pattern was shifted towards V3 in untreated rats with CHF, and was shifted back towards V1 in the captopril-treated rats. In the clinical study, captopril (37.5–75 mg/day) was administered to patients with cardiomyopathy for 12 months. There was no effect on left ventricular mass in hypertrophic cardiomyopathy, although systolic anterior motion of the mitral valve disappeared in one patient. In dilated cardiomyopathy, however, left ventricular mass tended to decrease. These results indicate that captopril has a beneficial effect in congestive heart failure. 相似文献
49.
Shunya Sogon Shinji Imakawa Makoto Masutani Nobuyoshi Takeuchi Katsuhiko Kubo 《Journal of Ethology》1993,11(1):1-10
The purposes of this study were two-fold. First, it compared Japanese infants' (N=129) abilities to regulate emotions at 13
months and 18 months of age, using the Strange Situation procedure. Second, it examined the relationship between the development
of emotion regulation and the mother's emotion expression style as assessed by the Emotion Expression Style Questionnaire
(EESQ). The total number of subjects who successfully completed all 8 episodes of the Strange Situation procedure increased
significantly during the aging between 13 and 18 months of age, indicating that as a group these infants increased their ability
to cope with stressful situations. However, infants who had mothers with negative emotion expression styles did not show greater
capacity for emotion regulation at 18 months. These findings suggest that the development of emotion regulation is mediated
by the mother's emotion expression style. 相似文献
50.
Abstract Polymerase chain reaction was carried out to amplify the conserved region (789 bp in the case of Mycoplasma capricolum ) of the dnaA gene (1350 bp in the case of M. capricolum ) of 15 representatives of the class Mollicutes using degenerate oligonucleotide primers. The dnaA gene fragments were amplified from M. mycoides subsp. capri, Spiroplasma apis and S. citri . The amino acid sequences deduced from the nucleotide sequences of the amplified fragments showed very low similarities to those of the corresponding regions of four walled bacteria. The values of similarity between any two of the three mollicute species were lower than those between any two of the four walled bacteria. 相似文献