全文获取类型
收费全文 | 3295篇 |
免费 | 195篇 |
国内免费 | 5篇 |
专业分类
3495篇 |
出版年
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 45篇 |
2020年 | 21篇 |
2019年 | 26篇 |
2018年 | 43篇 |
2017年 | 27篇 |
2016年 | 53篇 |
2015年 | 119篇 |
2014年 | 149篇 |
2013年 | 200篇 |
2012年 | 234篇 |
2011年 | 228篇 |
2010年 | 152篇 |
2009年 | 154篇 |
2008年 | 215篇 |
2007年 | 235篇 |
2006年 | 219篇 |
2005年 | 253篇 |
2004年 | 217篇 |
2003年 | 186篇 |
2002年 | 188篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 41篇 |
1998年 | 52篇 |
1997年 | 32篇 |
1996年 | 34篇 |
1995年 | 33篇 |
1994年 | 39篇 |
1993年 | 23篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 22篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有3495条查询结果,搜索用时 0 毫秒
21.
22.
When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO3,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O2 evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO-3, and algae grown or adapted to a low, air-levelCO2 in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO2 in air. Photosynthetic O2 evolutionwithout alkalization occurred using either internal DIC or externalCO2 at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO3 into CO2 plus OH during photosynthesisby cells with a high affinity for CO2 uptake. Cells grown onhigh CO2 to suppress the DIC pump, when given low levels ofHCO3 in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO3 pump, aswell as a CO2 pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O2 evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H2CO3 to HCO3 and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO2 concentrating process.
1Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan. 相似文献
23.
Teruyo Ito Keiichi Hiramatsu Yoshihiro Ohshita Takeshi Yokota 《Microbiology and immunology》1993,37(4):281-288
In cultures of Vibrio cholerae strains of Ogawa serotype, variant strains which had undergone serotype conversion from Ogawa to Inaba were identified. The rfbT genes cloned from the parent strains were found to produce a 31-kDa protein in the maxicell system, and to cause serotype conversion when introduced into E. coli cells expressing Inaba serotype specificity. On the other hand, rfbT genes cloned from the variant strains neither produced the 31-kDa protein nor caused serotype conversion. Nucleotide sequence of these rfbT genes as well as those of two clinical Vibrio cholerae strains of Inaba serotype revealed that mutations causing premature termination of their rfbT genes were invariably present in strains expressing Inaba serotype specificity. The result strongly suggested that genetic alteration of the rfbT gene is responsible for serotype conversion of Vibrio cholerae O1. 相似文献
24.
Yoshihiro Izumi Kanji Ono Masayuki Takamiya Kiichi Fukui 《Journal of plant research》1993,106(4):319-325
Using cultured cells of the hornwortAnthoceros punctatus, the change in the relative chloroplast DNA content in each stage of chloroplast division was investigated to clarify the
relationship between the division cycle of a chloroplast and a cell nucleus. Samples of cultured cells were stained with 4′,6-diamidino-2-phenylindole
(DAPI) and then observed with an epifluorescence microscope and a chromosome image analyzing system (CHIAS). A chloropiast
in cultured cells duplicated DNA with an increase in size. When a chloroplast began to divide, it was constricted in the middle,
taking a dumbbell shape, and then divided into two daughter chloroplasts. In cultured cells of this species, the pattern of
quantitative change of chloroplast DNA, that is, the DNA replication pattern of chloroplasts, corresponded to that of cell
nuclear DNA in mitosis. 相似文献
25.
Isao Sakita Takushi Monden Hirohito Nagaoka Yoshihiro Katsumoto Taro Wakasugi Naohiro Tomita Tsutomu Takeda Tetsuro Kobayashi Takashi Shimano Takesada Mori 《Biotherapy》1993,6(2):103-112
We have previously reported that the antitumor effect of OK-432, a streptococcal preparation, is markedly augmented when injected intratumorally together with fibrinogen (OK-432/fbg) [1]. In order to elucidate the effects of this immunotherapy on regional lymph nodes (RLN), we carried out both morphological and functional analyses of the RLN from colonic cancer patients treated with OK-432/ fbg. Computer-aided morphometry revealed that the maximal cross-sectional areas and the broadest diameters of the RLN were significantly greater (p<0.01) in patients who had undergone local immunotherapy than in patients who had not. The component structures of RLN, such as sinus, follicle and paracortex, were all enlarged in the OK-432/fbg-treated patients, and necrosis of metastatic tumors was observed. RLN lymphocytes recovered from OK-432/fbg treated patients showed elevated reactivity to phytohemagglutinin (PHA) and the stimulation index was clearly higher than that of control patients. Flow cytometric analysis revealed a predominance of T-cells, especially CD4 subsets, and higher positivity for both CD25 and HLA-DR. Furthermore, RLN lymphocytes killed more effectively K562 and Daudi cells in the patients who had had immunotherapy. These results suggest that the effect of local immunotherapy with OK-432/fbg is not restricted to the site of injection but extends to the lymph nodes, and contributes to tumor regression through the augmentation of cellular immunity.Abbreviations RLN
regional lymph node(s)
- OK-432/fbg
OK-432/fibrinogen solution
- PHA
phytohemagglutinin
- NK
natural killer
- LAK
lymphocyte activated killer 相似文献
26.
Yoshihiro Takasugi Keiji Kawata Takahiko Okuda Yoshihisa Koga Nobuyuki Mizuguchi Shigeaki Yamanaka Shinsuke Watanabe 《Experimental Animals》2003,52(5):429-432
Age-related alterations and differences of weights and those of amino acid concentrations in the cerebrospinal fluid (CSF) were evaluated between Sprague Dawley (SD) rats and Wistar Kyoto (WKY) rats from eight to twenty weeks of age. The weights of SD rats were heavier than WKY rats at all ages. The age-related alterations of the CSF concentration of many amino acids within each strain were significant but showed no significant trend with age. Between the strains, the concentration differences of excitatory and inhibitory amino acids were not frequent although the concentrations of arginine, alanine and threonine were significantly higher in SD rats than in WKY rats. These results suggest that the different CSF concentrations of amino acids may relate to characteristics of rat strains. 相似文献
27.
Yoshihiro Kuroda Yoshitaka Maeda Shinichi Sawa Kiyohiro Shibata Kazuhide Miyamoto Terumichi Nakagawa 《Journal of peptide science》2003,9(4):212-220
Pathogenic prion proteins (PrP(Sc)) are thought to be produced by alpha-helical to beta-sheet conformational changes in the normal cellular prion proteins (PrP(C)) located solely in the caveolar compartments. In order to inquire into the possible conformational changes due to the influences of hydrophobic environments within caveolae, the secondary structures of prion protein peptides were studied in various kinds of detergents by CD spectra. The peptides studied were PrP(129-154) and PrP(192-213); the former is supposed to assume beta-sheets and the latter alpha-helices, in PrP(Sc). The secondary structure analyses for the CD spectra revealed that in buffer solutions, both PrP(129-154) and PrP(192-213) mainly adopted random-coils (approximately 60%), followed by beta-sheets (30%-40%). PrP(129-154) showed no changes in the secondary structures even in various kinds of detergents such as octyl-beta-D-glucopyranoside (OG), octy-beta-D-maltopyranoside (OM). sodium dodecyl sulfate (SDS), Zwittergent 3-14 (ZW) and dodecylphosphocholine (DPC). In contrast, PrP(192-213) changed its secondary structure depending on the concentration of the detergents. SDS, ZW, OG and OM increased the alpha-helical content, and decreased the beta-sheet and random-coil contents. DPC also increased the alpha-helical content, but to a lesser extent than did SDS, ZW, OG or OM. These results indicate that PrP(129-154) has a propensity to adopt predominantly beta-sheets. On the other hand, PrP(192-213) has a rather fickle propensity and varies its secondary structure depending on the environmental conditions. It is considered that the hydrophobic environments provided by these detergents may mimic those provided by gangliosides in caveolae, the head groups of which consist of oligosaccharide chains containing sialic acids. It is concluded that PrP(C) could be converted into a nascent PrP(Sc) having a transient PrP(Sc) like structureunder the hydrophobic environments produced by gangliosides. 相似文献
28.
Tadayuki Miyamoto Susumu Kagawa Kouki Kitagawa Shiroh Futaki Hiromichi Yokoi Yoshihiro Tsuruo Kazunori Ishimura 《Histochemistry and cell biology》1996,105(2):101-109
We immunohistochemically studied the localization of 5-reductase type 1 in combination with androgen receptor (AR) expression in individual lobes of the prostates of intact and castrated rats. In the normal rat prostate, 5-reductase was localized in the cytoplasm of most epithelial cells in the ventral, dorsal, and lateral type 1 (L1) lobes. Epithelial cells of lateral type 2 (L2) lobes were negative for 5-reductase. AR was present in the nuclei of all epithelial and stromal cells throughout the prostate. The number of 5-reductase-immunoreactive cells rapidly decreased in the ventral and L1 lobes after castration, whereas many positive cells remained in the dorsal lobe even at 4 weeks after castration. AR immunostaining was lost in the ventral, dorsal, and L1 lobes at 1 week after castration, but remained in the L2 lobe of 4-week-castrated rats. Electron microscopic immunocytochemistry showed that 5-reductase was exclusively localized in the rough endoplasmic reticulum membranes and that there were no distinct structural differences between the positively and negatively stained epithelial cells. These findings suggested that the expression of 5-reductase type 1 in the epithelial cell is heterogeneous within and among the individual lobes of the rat prostate, and does not correspond to AR expression. 相似文献
29.
Eight diatom species (Chaetoceros pseudocurvisetus Mang ., Stephanodiscus hantzschii Grun ., Skeletonema costatum ( Grev.) Cleve , Asterionella formosa Hass ., Thalassiosira nordenskioeldii Cleve , Detonula confervacea ( Cleve) Gran , Chaetoceros sp., and Nitzschia frigida Grun.) were isolated from various temperature environments ranging from temperate to the Arctic, and their growth responses to temperature were determined. Each species grew over a different temperature range. The lower and upper limits of each species varied from −1.8° to 20° C and from 2° to 30° C, respectively. The width of the growth range of each species. also varied from 3.8° to 25° C, and the growth of these species was observed, as a whole, between a wide temperature range from −1.8° to 30° C .
Within the growth temperature ranges, the growth rate of each species increased with temperature until reaching a maximum, which was followed by a steep decrease up to the upper limit of the growth range. As a result, each species showed a maximum rate at the temperature very near to the upper limit, which was generally higher than the isolation temperature. The specific growth rates were compared among the eight species. The interspecific maximum rate at each temperature exhibited an exponential increase with a Q10 = 1.48. The relative growth rates of each species were calculated by normalizing the specific growth rates with the interspecific maximum rate at each respective temperature. The higher relative growth rates tended to occur at the isolation temperature of each species, suggesting that temperature is a significant control on species distributions in nature . 相似文献
Within the growth temperature ranges, the growth rate of each species increased with temperature until reaching a maximum, which was followed by a steep decrease up to the upper limit of the growth range. As a result, each species showed a maximum rate at the temperature very near to the upper limit, which was generally higher than the isolation temperature. The specific growth rates were compared among the eight species. The interspecific maximum rate at each temperature exhibited an exponential increase with a Q
30.
Molecular cloning of two tandemly arranged peroxidase genes from Populus kitakamiensis and their differential regulation in the stem 总被引:2,自引:0,他引:2
Keishi Osakabe Hirokazu Koyama Shinya Kawai Yoshihiro Katayama Noriyuki Morohoshi 《Plant molecular biology》1995,28(4):677-689
A genomic library was prepared from Populus kitakamiensis and screened with the cDNA for an anionic peroxidase from P. kitakamiensis. One genomic clone was isolated that contained two tandemly oriented genes for anionic peroxidases, prxA3a and prxA4a. Both genes consisted of four exons and three introns; the introns had consensus nucleotides, namely, GT and AG, at their 5 and 3 ends, respectively. The prxA3a and prxA4a genes encoded 347 and 343 amino acid residues, respectively, including putative signal sequences at the amino-termini. Putative promoters and polyadenylation signals were found in the flanking regions of both genes. The sequence of the coding region of prxA3a was completely identical to that of the cDNA clone pA3, whereas the sequence of the coding region of prxA4a was only 73% identical to that of the cDNA clone pA3. Northern blot analysis showed that the patterns of expression of the mRNAs that corresponded to prxA3a and prxA4a differed in stems of P. kitakamiensis. 相似文献