全文获取类型
收费全文 | 2593篇 |
免费 | 121篇 |
国内免费 | 2篇 |
专业分类
2716篇 |
出版年
2023年 | 5篇 |
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 64篇 |
2015年 | 66篇 |
2014年 | 99篇 |
2013年 | 215篇 |
2012年 | 142篇 |
2011年 | 166篇 |
2010年 | 100篇 |
2009年 | 82篇 |
2008年 | 122篇 |
2007年 | 130篇 |
2006年 | 153篇 |
2005年 | 160篇 |
2004年 | 152篇 |
2003年 | 155篇 |
2002年 | 150篇 |
2001年 | 54篇 |
2000年 | 40篇 |
1999年 | 40篇 |
1998年 | 40篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 29篇 |
1994年 | 32篇 |
1993年 | 10篇 |
1992年 | 41篇 |
1991年 | 26篇 |
1990年 | 33篇 |
1989年 | 17篇 |
1988年 | 31篇 |
1987年 | 23篇 |
1986年 | 33篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有2716条查询结果,搜索用时 0 毫秒
1.
A new phosphorylating agent, S-(N-monomethoxytritylaminoethyl)-O-(O-chlorophenyl) phosphorothioate, was prepared and reacted with a 5'-hydroxyl group of an oligonucleotide using 1-mesitylene-sulfonyl-3-nitrotriazole (MSNT) as a condensing agent. After base labile protecting groups were removed, the partially deprotected oligonucleotide was separated on a reversed phase column and converted to the oligonucleotide with an aminoethyl or a phosphoryl group at the 5'-end by treatment with 80% acetic acid or iodine-water, respectively. The syntheses of ppT, pppT, A5'pp5'T and A5'ppp5'T were also performed by treatment of 5'-O-(N-monomethoxytritylaminoethylthiophosphoryl) thymidine with tri-n-octylammonium salt of phosphoric acid, pyrophosphoric acid, pA and ppA, respectively. 相似文献
2.
Twelve healthy male volunteers were given theophylline 250 mg in order to test effects on 24-hr rhythms. Rhythms of sleep/wake and subjective sleepiness were delayed. Ingestion of xanthines such as theophylline in coffee, tea, colas and chocolate may contribute to some sleep disorders. Theophylline might likewise be useful in treating disorders of circadian oscillators. 相似文献
3.
Rosa Sorrentino Carlo Iannicola Sandro Costanzi Giulio Ratti Carolyn Hurley Roberto Tosi Nobuyuki Tanigaki 《Immunogenetics》1990,32(1):8-12
TR81 is a specificity closely related to or identical with DR3. In Caucasoids two amino acids, Tyr at position 26 and Arg at position 74 of HLA class II DR chains, have been found to be associated with the presence of TR81. Recently, a variant of DRBI *03 identified in American Blacks has been shown to possess Arg at position 74 but Phe at position 26. This codon combination is found to be present in four other cell lines where it still specifies the TR81 determinant. This suggests that the TR81 specificity is uniquely dependent on the presence of Arg at position 74. 相似文献
4.
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
5.
Optimal strategy of plant antiherbivore defense: Implications for apparency and resource-availability theories 总被引:3,自引:0,他引:3
Plants produce chemicals as methods against animal herbivory. Such chemical defenses are classified into two major categories:
(i) quantitative defenses with massive production of indigestible substances; and (ii) qualitative defenses with production
of poisonous substances. A mathematical model was developed that identified factors that favored the evolution of quantitative
defenses. Selecting an annual plant for simplicity, the allocation of photosynthetic production between growth substances
and defense substances was considered. If the plant invests more in defense substances, it can protect itself more efficiently
from herbivory but with a reduced growth rate. If it invests more in growth substances, the contrary holds. Using Pontoryagin's
maximum principle, the following results were obtained: (i) the plant should conduct quantitative defenses when the growth
rate (G), reflecting resource-availability, is low and the growth period (T) is long as well; (ii) if the plant invests in quantitative defenses, the optimal proportion of defense substances (χ*) should be higher asG is smaller, but it is independent ofT; and (iii) the value of χ* is not monotone for the effectiveness of defense substance (A), but has a maximum at an intermediate value ofA. Predictions of the model partly supported both Feeny's apparency theory, claiming that apparent plants or their parts for
herbivores should quantitatively defend themselves, and Coley's resource-availability theory, claiming that plants with rich
resources should invest in growth rather than defense. 相似文献
6.
Shigenobu Kanba Nobuyuki Sasakawa Toshio Nakaki Kiyoko-Shimizu Kanba Gohei Yagi Ryuichi Kato Elliott Richelson 《Journal of neurochemistry》1991,57(6):2011-2015
Prostaglandin E1 (PGE1)-mediated transmembrane signal control systems were investigated in intact murine neuroblastoma cells (clone N1E-115). PGE1 increased intracellular levels of total inositol phosphates (IP), cyclic GMP, cyclic AMP, and calcium ([Ca2+]i). PGE1 transiently increased inositol 1,4,5-trisphosphate formation, peaking at 20 s. There was more than a 10-fold difference between the ED50 for PGE1 at cyclic AMP formation (70 nM) and its ED50 values at IP accumulation (1 microM), cyclic GMP formation (2 microM), and [Ca2+]i increase (5 microM). PGE1-mediated IP accumulation, cyclic GMP formation, and [Ca2+]i increase depended on both the concentration of PGE1 and extracellular calcium ions. PGE1 had more potent intrinsic activity in cyclic AMP formation, IP accumulation, and cyclic GMP formation than did PGE2, PGF2 alpha, or PGD2. A protein kinase C activator, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, had opposite effects on PGE1-mediated IP release and cyclic GMP formation (inhibitory) and cyclic AMP formation (stimulatory). These data suggest that there may be subtypes of the PGE1 receptor in this clone: a high-affinity receptor mediating cyclic AMP formation, and a low-affinity receptor mediating IP accumulation, cyclic GMP formation, and intracellular calcium mobilization. 相似文献
7.
Nobuyuki Inagaki Hiroaki Nishimura Minoru Okada Hiroshi Mitsuhashi 《Plant cell reports》1991,9(9):484-487
Verbascoside was found to be produced in all calli derived from eleven species that contained the compound in their leaves. Cell suspension cultures were also established in three species, i.e., Leucosceptrum japonicum f. barbinerve, Syringa josikaea, and Sy. vulgaris, all of which were found to produce verbascoside at more than 1 g/l. Of the three species, suspension cultures of L. japonicum f. barbinerve showed rapid growth and the highest yield of verbascoside (1.89 g/l). In these cultures, the effects of major salt concentration in B5 medium on cell growth and verbascoside production were examined. Maximum cell growth and maximum verbascoside production were both achieved by reducing the major salt concentration to half that of the original medium. 相似文献
8.
H Sakata K Yamanouchi K Machida F Matsuzaki A Shishido H Iwashita Y Kuroiwa 《Japanese journal of medical science & biology》1979,32(2):67-76
A highly sensitive procedure of solid-phase radioimmunoassay (RIA) was developed for the detection of measles IgG antibody. HeLa cells persistently infected with measles virus were used as a solid-phase antigen. This technique was applied to the detection of measles IgG antibody in patients with subacute sclerosing panencephalitis (SSPE) and multiple sclerosis. Normal subjects having experienced natural measles or measles vaccination and patients with various neurological diseases of non-virus nature were also examined as control groups. Measles antibody was detected at high titers in both the sera and cerebrospinal fluid of SSPE patients. Moreover, RIA/HI ratios of SSPE patients were significantly higher than those of normal subjects, suggesting the presence in the formers of antibodies to nucleocapsids at high titers as well as to viral envelopes. On the other hand, no significant difference was found in both RIA and HI titers between the sera of multiple sclerosis and those of various neurological diseases. 相似文献
9.
Nobuyuki Itoh Ikuo Yamashina 《Biochemical and biophysical research communications》1975,67(2):840-845
Taka amylase A glycopeptide (TA-GP) strongly inhibited the interaction of antimannan (antibodies directed towards mannan from ) with yeast mannan, whereas ovalbumin glycopeptide (OA-GP) did so only poorly. We inferred that this is due to the strong reactivity of antimannan with terminal trimannosides composed of Manα1→2Man or Manα1→3Man linkages which occur in mannan and TA-GP. In contrast, TA-GP and OA-GP were nearly equally reactive with concanavalin A having the ability to interact with terminal mannose and 2-0-mannose residues which occur abundantly in these glycopeptides. Thus, antimannan should be useful as a probe for characterizing glycoproteins from extracellular fluids or cellular membranes. 相似文献
10.
Oarada M Tsuduki T Suzuki T Miyazawa T Nikawa T Hong-quan G Kurita N 《Biochimica et biophysica acta》2003,1622(3):151-160
The effect of dietary docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on host resistance to Paracoccidioides brasiliensis infection was investigated. Mice fed palm oil supplemented with DHA showed reduced antifungal activity in the spleen and liver, as compared with mice fed palm oil or soybean oil without supplementation with DHA. Mice fed DHA-supplemented soybean oil also showed reduced antifungal activity in the liver, but the extent of reduction was less profound. This reduction in antifungal activity was not observed with EPA-supplemented palm or EPA-supplemented soybean oil. These results suggest that two factors, DHA and palm oil in combination, are involved in reducing the host resistance. DHA-enriched palm oil was also responsible for an increase in DHA concentration and a marked decrease in arachidonic acid content in the spleen and liver. However, this group did not show elevated spleen and liver phospholipid hydroperoxide levels compared with the other groups, excluding the possibility that the reduction in antifungal activity observed with DHA-enriched palm oil is due to acceleration of in vivo lipid peroxidation. Greater infection-induced increases in spleen and serum interferon-gamma concentrations were observed in mice fed DHA-enriched palm oil compared with the other groups. 相似文献