全文获取类型
收费全文 | 8017篇 |
免费 | 477篇 |
国内免费 | 3篇 |
出版年
2023年 | 20篇 |
2022年 | 57篇 |
2021年 | 108篇 |
2020年 | 56篇 |
2019年 | 90篇 |
2018年 | 104篇 |
2017年 | 116篇 |
2016年 | 152篇 |
2015年 | 278篇 |
2014年 | 306篇 |
2013年 | 527篇 |
2012年 | 500篇 |
2011年 | 497篇 |
2010年 | 362篇 |
2009年 | 319篇 |
2008年 | 533篇 |
2007年 | 511篇 |
2006年 | 533篇 |
2005年 | 507篇 |
2004年 | 498篇 |
2003年 | 494篇 |
2002年 | 482篇 |
2001年 | 85篇 |
2000年 | 79篇 |
1999年 | 119篇 |
1998年 | 107篇 |
1997年 | 84篇 |
1996年 | 76篇 |
1995年 | 70篇 |
1994年 | 81篇 |
1993年 | 74篇 |
1992年 | 59篇 |
1991年 | 53篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 44篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 34篇 |
1984年 | 38篇 |
1983年 | 26篇 |
1982年 | 39篇 |
1981年 | 35篇 |
1980年 | 19篇 |
1979年 | 29篇 |
1978年 | 13篇 |
1977年 | 29篇 |
1976年 | 12篇 |
1973年 | 18篇 |
1972年 | 15篇 |
排序方式: 共有8497条查询结果,搜索用时 31 毫秒
71.
72.
Yamazaki Masaaki; Ono Ayako; Watanabe Koji; Sasaki Kuniaki; Tashiro Hiroyuki; Nomura Toru 《DNA research》1995,2(4):187-189
Most ofthe human Not I linking clones identified to date areconsidered to be derived from CpG islands because ofthe recognitionsequence of this enzyme, and CpG islands have been reportedto be located around the 5' regions of genes. As a pilot study,we determined the complete nucleotide sequence (41,924 bp) ofa human cosmid clone (LL21NC02Q7A10) containing the marker D21S246originating from a Not I linking clone. As a result of sequenceanalysis, we successfully mapped and revealed the genomic genestructure for KIAA0002 previously reported as a cDNA clone.This gene consists of 15 exons and was shown to exist at theD21S246 locus on human chromosome 21q21.3q22.1. Theseresults demonstrated that genomic marker-anchored DNA sequencingis a useful approach for the human genome project. 相似文献
73.
Shinji Tokuyama Hiroyuki Miya Kazunori Hatano Takeshi Takahashi 《Applied microbiology and biotechnology》1994,40(6):835-840
A novel enzyme, N-acylamino acid racemase, was purified to homogeneity from Streptomyces atratus Y-53 and characterized. This enzyme catalyzes the interconversion of optically active N-acylamino acids. The relative molecular mass (Mr) of the enzyme was estimated to be about 41 000 and 244 000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration, respectively, indicating that the enzyme is composed of six subunits with an equal Mr. The enzyme showed a broad substrate specificity toward N-acylamino acids, such as N-acetylmethionine, N-chloroacetylphenylalanine and N-chloroacetylvaline. The apparent Michaelis constant (Km) values for N-acetyl-l-methionine and N-acetyl-d-methionine were calculated to be 15.2 and 5.6 mm, respectively. Enzyme activity was markedly enhanced by divalent metal ions, such as Co2+, Mg2+ and Mn2+, and was inhibited by metal-chelating reagent, indicating that the enzyme is a metalloenzyme. We propose to name the enzyme N-acylamino acid racemase (acylamino acid racemase).
Correspondence to: S. Tokuyama 相似文献
74.
The reason for failure to initiate fertilization internally was examined in a cottid fish, the elkhorn sculpin, Alcichthys alcicornis which has internal gametic association and external fertilization. While eggs could be activated in calcium free hypertonic media but not be fertilized, fertilization occurred in isotouic media rich in calcium ions. The rate of fertilization was dependent on calcium concentration, and eggs were not fertilized in solutions with a calcium ion concentration of less than 0·57 mmol kg−1 . Calcium ions could be replaced to some extent by magnesium ions, but the former were the more effective in fertilization. Since calcium ion concentration of ovarian fluid of A. alcicornis was 0·41 mmol kg−1 , it was inferred that low calcium concentration in the ovarian fluid was the cause of the failure of A. alcicornis eggs to fertilize internally. 相似文献
75.
The expression of two regeneration-associated antigens in the blastemas of normal and retinoid-treated regenerating limbs of axolotl ( Ambystoma mexicanum ) was examined.
One antigen, 55C12, which was similar to tenascin in expression pattern and molecular weight profile, was weakly expressed in the perichondrium and tendon of normal limbs. In the regenerating limbs, the amount of 55C12 antigen increased near the amputation site within 7 days and almost all cells of the blastema mesenchyme came to be positive to the antigen at 20 days, although those of epidermis and most stump tissues were negative. When the regenerating limbs were treated with Am80, a synthetic retinoid, which induced proximo-distal duplication, the expression of 55C12 antigen in the blastema became weak temporarily and was reactivated in the anterior region of the blastema. This expression pattern suggests that the duplicated limb is formed by the preferential growth of this 55C12-positive anterior blastema region.
The other antigen, 117C1, was faintly expressed in the epidermis, dermis, muscle, perichondrium and cartilage of normal limbs, and intensely expressed in the blastema mesenchyme and wound epidermis. The Am80 treatment, however, induced no changes in the expression pattern of 117C1.
These results suggest that these antigens may distinguish two different regions of the blastema in normal regeneration and retinoid-induced duplication. 相似文献
One antigen, 55C12, which was similar to tenascin in expression pattern and molecular weight profile, was weakly expressed in the perichondrium and tendon of normal limbs. In the regenerating limbs, the amount of 55C12 antigen increased near the amputation site within 7 days and almost all cells of the blastema mesenchyme came to be positive to the antigen at 20 days, although those of epidermis and most stump tissues were negative. When the regenerating limbs were treated with Am80, a synthetic retinoid, which induced proximo-distal duplication, the expression of 55C12 antigen in the blastema became weak temporarily and was reactivated in the anterior region of the blastema. This expression pattern suggests that the duplicated limb is formed by the preferential growth of this 55C12-positive anterior blastema region.
The other antigen, 117C1, was faintly expressed in the epidermis, dermis, muscle, perichondrium and cartilage of normal limbs, and intensely expressed in the blastema mesenchyme and wound epidermis. The Am80 treatment, however, induced no changes in the expression pattern of 117C1.
These results suggest that these antigens may distinguish two different regions of the blastema in normal regeneration and retinoid-induced duplication. 相似文献
76.
Rhodium-catalyzed synthesis of 2(5H)-furanones from alkynes under water-gas shift reaction conditions was studied. By improving the reaction conditions for internal alkynes reported previously, the reaction could be extended to terminal alkynes. Terminal alkynes are selectively converted into 3- and 4-substituted 2(5H)-furanones (2 and 3). When acetylene itself is used, 2(5H)-furanone (2n) is obtained in a good yield. Examination of reaction solutions by IR spectroscopy and some other experimental findings suggest that the active species would be an alkyne-coordinated monomeric rhodium anion. A new reaction path is proposed. 相似文献
77.
Ritsuko Katoh-Semba Reiji Semba Hiroyuki Kato† Masataka Ueno† Yoshihiro Arakawa† Kanefusa Kato‡ 《Journal of neurochemistry》1994,62(6):2141-2147
Abstract: Our previous studies showed that the concentration of the β subunit of nerve growth factor (β-NGF) in nervous tissues is higher in male than in female mice. To identify the brain regions that are affected by androgens, the amounts of β-NGF protein and its mRNAs were measured in male, female, and castrated male CD-1 mice and testicular feminization mice at 3–4 months of age. Among tissues examined, the hypophysis of males contained the highest average concentration of β-NGF protein. In most regions of the brain, individual levels were more variable in males than in females. However, after the castration, such variations in β-NGF levels disappeared. Average levels of β-NGF protein in males were higher in the cerebellum (eightfold higher), olfactory bulb (12-fold higher), hypothalamus (sixfold higher), and hypophysis (72-fold higher) than thope in corresponding regions of females. No significant differences were observed in levels of β-NGF protein in the hippocampus, cerebral cortex, striatum, septum, and brainstem. The castration of male mice caused a reduction in levels of β-NGF protein in the hypothalamus and hypophysis, but not in the cerebellum and olfactory bulb, to the femgle levels. The concentrations of β-NGF protein in testicular feminization mice were similar to those in female CD-1 mice in all regions. The concentrations of mRNA for β-NGF in the olfactory bulb and hypophysis from males were higher than those from females. By contrast, northern blots showed no remarkable differences in the amounts of brain-derived neurotrophic factor and neurotrophin-3 between the two sexes. Thus, in some regions of the brain, the production of β-NGF appears to be regulated by testosterone, but the regulatory mechanisms do not appear to be simple. Our present results indicate that the binding of testosterone to its receptor is an important step in the regulation of the level of β-NGF in these region. 相似文献
78.
Hiroyuki Kamachi Noriaki Tamura Takashi Yoshihira Tatsuo Oku 《Physiologia plantarum》1994,91(4):747-753
Photosystem II membranes (D-PSII) were isolated from dark-grown spruce seedlings. All major PSII proteins except the 17- and 23-kDa extrinsic proteins were present in D-PSII. O2 evolution and Mn content in D-PSII were negligible, while PSII-donor activity showed a value comparable to that of NH2 OH-treated PSII membranes (NH2 OH-L-PSII) from light-grown seedlings. Light incubation of D-PSII with 1 m M MnCl2 , 50 m M CaCl2 and 100 μ M DCIP at pH 5.3 resulted in activation of the latent water-oxidizing complex. Accomplishment of photoactivation of PSII membranes from dark-grown spruce seedlings clearly indicates that only ligation of Mn2+ to the apo-water oxidizing complex is required for expression of O2 evolution, and that protein synthesis is not involved in the photoactivation process. There was no essential difference between 'photoactivation' of naturally Mn-free PSII membranes and 'photoreactivation' of artificially Mn-depleted PSII membranes on kinetics, pH dependence, Mn2+ -concentration dependence. However, kinetics and pH dependence of photoactivation were appreciably different in spruce PSII membranes and in PSII membranes of angiosperms such as wheat and spinach. 相似文献
79.
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
80.
John G. Frazier Harry L. Fierstine Sallie C. Beavers Federico Achaval Hiroyuki Suganuma Robert L. Pitman Yuichiro Yamaguchi Carlos Ma. Prigioni 《Environmental Biology of Fishes》1994,39(1):85-96
Synopsis Billfishes have long been known to impale a great variety of objects, but there are only two brief, obscure records of marine
turtles being speared. Details are presented on these two, as well as on two other confirmed records; data from two additional
unconfirmed records are also presented. In total, three species of marine turtles are known to have been impaled by three
species of billfishes; a fourth species of fish and a fourth species turtle are listed in an unconfirmed case. Records come
from the eastern and western Pacific as well as the eastern Atlantic. Of the four confirmed cases, the turtles survived in
two, and apparently died as an effect of the spearing in the other two. In three confirmed cases only the impaled rostrum
was encountered, and in one confirmed case the entire fish was found, with its rostrum piercing the turtle. There is no obvious
advantage — or clear disadvantage — involved in impaling turtles. It is argued that these attacks are accidental, and the
result of attempts made by the billfish to capture prey that are near the turtle. These spearings indicate that the chelonians
serve as shelters for prey animals on the high seas, and thus, are further evidence of the pelagic existence of marine turtles.
The impalings are evidence of a singular ecological role of the turtles — as live fish aggregation devices. 相似文献