全文获取类型
收费全文 | 1650篇 |
免费 | 75篇 |
国内免费 | 1篇 |
专业分类
1726篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 24篇 |
2018年 | 27篇 |
2017年 | 15篇 |
2016年 | 43篇 |
2015年 | 62篇 |
2014年 | 68篇 |
2013年 | 106篇 |
2012年 | 129篇 |
2011年 | 99篇 |
2010年 | 66篇 |
2009年 | 54篇 |
2008年 | 128篇 |
2007年 | 109篇 |
2006年 | 83篇 |
2005年 | 91篇 |
2004年 | 98篇 |
2003年 | 90篇 |
2002年 | 98篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有1726条查询结果,搜索用时 15 毫秒
1.
Yusuke Nakamura Michio Ogawa Takahiro Nishide Mitsuru Emi Goro Kosaki Seiichi Himeno Kenichi Matsubara 《Gene》1984,28(2):263-270
The nucleotide sequences of the cloned human salivary and pancreatic α-amylase cDNAs correspond to the continuous mRNA sequences of 1768 and 1566 nucleotides, respectively. These include all of the amino acid coding regions. Salivary cDNA contains 200 bp in the 5′-noncoding region and 32 in the 3′-noncoding region. Pancreatic cDNA contains 3 and 27 bp of 5′- and 3′-noncoding regions, respectively. The nucleotide sequence humology of the two cDNAs is 96% in the coding region, and the predicted amino acid sequences are 94% homologous.Comparison of the sequences of human α-amylase cDNAs with those previously obtained for mouse α-amylase genes (Hagenbuchle et al., 1980; Schibler et al., 1982) showed the possibility of gene conversion between the two genes of human α-amylase. 相似文献
2.
In temperate waters of southern Japan, mouthbrooding males of the cardinal fish Apogon doederleini sometimes ate their entire brood within a day of spawning. In spite of annual variation in age structure and length of the breeding season, however, the annual cannibalism rate (broods cannibalized to total broods spawned) was nearly constant, 12–16%. Fish 1 year old frequently cannibalized early broods of the season, especially the first brood, whereas the cannibalism rate by 2 year-old fish did not vary within the season. In contrast, the cannibalism by older males increased late in the season. This tendency was attributed to their different allocation patterns to growth and reproduction. For 1 year-old fish, which can enhance future reproductive success by growth and cannibalizing on early broods instead of mouthbrooding (at relatively low temperatures), this may be a tactic for investing energy in growth. For fish 3 years, which have more breeding cycles and grow little, cannibalizing late broods may be energetic compensation for their poor somatic condition. No seasonal variation of cannibalism by 2 year-old fish can be explained by their intermediate nature of growth and reproduction. Multiple mate availability is one factor facilitating the cannibalism by 2 and 3 + year-old fish whose operational sex ratio is female-biased. 相似文献
3.
Maternal care in the red-headed spruce web-spinning sawfly,Cephalcia isshikii (Hymenoptera: Pamphiliidae) 总被引:1,自引:0,他引:1
We describe oviposition and maternal behavior in the sawfly Cephalcia isshikiiand examine the adaptive significance of this behavior. Females deposited eggs in a single but loose cluster on needles of terminal twigs of spruces, Piceaspp., and remained with the eggs usually on the underside of the twig facing toward the tip. The female attended her eggs until death without taking food but did not follow the first-instar larvae that moved from natal needles even if she survived until then. When the female was disturbed, she usually moved toward the source and attempted to bite it. Though at much lower frequencies, this aggressive behavior was also observed in gravid females and even in males. Field observations and female removal experiments indicated that the female enhanced the survival of the eggs through the reduction of arthropod prédation. 相似文献
4.
N Sakai J Tamaoki K Kobayashi T Kanemura K Isono K Takeyama S Takeuchi T Takizawa 《Regulatory peptides》1991,34(1):33-41
We studied the effect of vasoactive intestinal peptide (VIP) on ciliary activity in rabbit cultured tracheal epithelium by a photoelectric method in vitro. Administration of VIP (10(-7) M) elicited an increase in ciliary beat frequency (CBF) from the baseline values of 970 +/- 52 to 1139 +/- 75 beats/min (mean +/- S.E., P less than 0.01). This ciliostimulatory effect was dose-dependent, with the maximal increase and EC50 value being 17.4 +/- 1.0% (P less than 0.05) and 6.10(-11) M, respectively. The VIP-induced increase in CBF was abolished by pretreatment of cells with [4-Cl-D-Phe6, Leu17]-VIP, a VIP receptor antagonist. The neutral endopeptidase inhibitor phosphoramidon (10(-5) M) potentiated the effect of VIP, so that the CBF dose-response curve for VIP was shifted to lower concentrations by 0.5 log U. The administration of VIP increased cyclic AMP levels in epithelial cells, an effect that was also potentiated by phosphoramidon. These results suggest that VIP may interact with its specific receptors and stimulate airway ciliary activity probably through the activation of adenylate cyclase, and that neutral endopeptidase may play a role in modulating this effect of VIP. 相似文献
5.
H Nakanishi H Ohyanagi Y Takeyama H Onoyama Y Saitoh A Kikuchi Y Takai 《Biochemical and biophysical research communications》1988,154(3):1314-1322
The incubation of isolated rat pancreatic acini with low doses (1 x 10(-11)-1 x 10(-10) M) of cholecystokinin-octapeptide (CCK8) induced amylase release. This CCK8-induced amylase release has been shown to be mediated through the protein kinase C activation and the Ca2+ mobilization which are linked to the phospholipase C-mediated hydrolysis of phosphoinositides. However, the incubation of the acini with high doses (1 x 10(-9)-1 x 10(-7) M) of CCK8 reduced amylase release to the level less than that induced by the maximally effective dose (1 x 10(-10) M) of this secretagogue. Under the same conditions, the high doses of this secretagogue did not inhibit the phospholipase C-mediated hydrolysis of phosphoinositides. The stimulatory action of the maximally effective dose of CCK8 in amylase release was mimicked by the simultaneous addition of protein kinase C-activating 12-O-tetradecanoylphorbol-13-acetate (TPA) and Ca2+ ionophore A23187. A high dose (1 x 10(-7) M) of CCK8 reduced the amylase release induced by the combination of TPA and A23187. These results suggest that the high doses of CCK8 inhibit the secretory process post to the protein kinase C-Ca2+ systems and thereby reduce the amylase release induced by the maximally effective dose of CCK8 in rat pancreatic acini. 相似文献
6.
In Swiss 3T3 cells, colon tumor-promoting deoxycholate (DOC) enhanced DNA synthesis which was induced by fibroblast growth factor (FGF) in the presence of insulin. This effect was observed only when DOC was added within 10 h after the addition of FGF. DOC by itself did not induce DNA synthesis irrespective of the presence or absence of insulin. Similar results were obtained with other colon tumor-promoting bile acids such as cholate, chenodeoxycholate and taurocholate. In contrast to these bile acids, 12-O-tetradecanoylphorbol-13-acetate (TPA) induced DNA synthesis fully without FGF in the presence of insulin. DOC did not affect TPA-induced DNA synthesis. Prolonged treatment of the cells with phorbol-12,13-dibutyrate caused the down-regulation of the phorbol ester receptor and rendered the cells unresponsive to TPA. In these cells, FGF still induced DNA synthesis in the presence of insulin, but the maximal level was reduced to about one third of that in the control cells. DOC did not enhance this DNA synthesis any more. DOC did not alter the binding of FGF to the cells. These results indicate that colon tumor-promoting bile acids enhance the mitogenic action of FGF and thereby stimulate DNA synthesis, although the phorbol ester substitutes for the mitogenic action of FGF. 相似文献
7.
H Yabumoto F Ikoma M Takeyama M Tsuji K Matsumoto 《Journal of steroid biochemistry》1985,22(4):495-499
We have reported [1-3] in immature golden hamster testis that 5 beta-reductase is localized in the tubular nongerm cells, while 5 alpha-reductase is present in the interstitial tissue and that the 17 beta-hydroxy-dehydrogenase activity is found predominantly in the tubular nongerm cells. Hormonal regulation of these enzyme activities was examined in the present study. Male golden hamsters were hypophysectomized on day 22 after birth. The hypophysectomized hamsters in groups of 3-8 were injected daily with 10 micrograms NIH-LH-S19, 50 micrograms NIAMD-Rat-FSH-B-1, 8 or 16 micrograms NIAMD-oFSH-13, 8 micrograms NIAMD-oFSH-13 plus 5 or 10 micrograms NIH-LH-S19, 1 mg testosterone propionate or saline for 5 days starting from day 23. Testicular homogenates of the treated hamsters and intact hamsters on day 28 were incubated with [14C]4-androstene-3,17-dione and NADPH, and enzyme activity (nmol/testes/h) was estimated. The activities of 5 beta- and 5 alpha-reductases and 17 beta-hydroxy-dehydrogenase decreased significantly 6 days after hypophysectomy. In the hypophysectomized hamster testis, a distinct response to FSH but not to LH in the activities of 5 beta-reductase and 17 beta-hydroxy-dehydrogenase was found. The injection of LH in addition to FSH showed no significant additive effects on these enzyme activities. The 5 alpha-reductase activity was stimulated significantly by LH plus FSH but not by LH alone, FSH alone or androgen. These results show that 5 beta-reduction of 4-ene-3-ketosteroids takes place in the Sertoli cells under the influence of FSH while 5 alpha-reduction occurs in the interstitial cells under the influence of LH and FSH in immature hamster testis. 相似文献
8.
9.
Kenichi Takaya 《Biotechnic & histochemistry》1967,42(4):207-211
The applicability of Luxol fast blue MBS as a 0.1% solution in 0.05% acetic acid to the staining of mitochondria, first recognized in rat kidney by Shanklin and Nassar (Stain Techn., 34: 257-60. 1959), was confirmed in various organs (formalin-Zenker and Regaud's fixations; paraffin embedding) of the mouse and bullfrog. In liver cells and in the epithelium of renal tubules, mitochondria were stained green, selectively and clearly. The dark cells of the renal tubules and the middle piece of sperms in both animals were conspicuously demonstrated by their dense assemblages of green granules. The periodic acid-Schiff procedure proposed by Shanklin and Nassar as a counterstain was replaced by staining in 0.5% aqueous phloxine, 2-3 min; differentiation in 5% phosphotungstic acid, 2 min; and washing in water, 5 min. This simplified and accelerated the techique, and gave a better color contrast. Advantages of Luxol fast blue MBS and phloxine staining over traditional methods for mitochondria in paraffin sections are: durability of the stain, high specificity, simplicity of procedure, and constant result. 相似文献
10.
M Jounouchi M Takeyama P Chaiprasert T Noumi Y Moriyama M Maeda M Futai 《Archives of biochemistry and biophysics》1992,292(2):376-381
The roles of the Escherichia coli H(+)-ATPase (FoFl) delta subunit (177 amino acid residues) was studied by analyzing mutants. The membranes of nonsense (Gln-23----end, Gln-29----end, Gln-74----end) and missense (Gly-150----Asp) mutants had very low ATPase activities, indicating that the delta subunit is essential for the binding of the Fl portion to Fo. The Gln-176----end mutant had essentially the same membrane-bound activity as the wild type, whereas in the Val-174----end mutant most of the ATPase activity was in the cytoplasm. Thus Val-174 (and possibly Leu-175 also) was essential for maintaining the structure of the subunit, whereas the two carboxyl terminal residues Gln-176 and Ser-177 were dispensable. Substitutions were introduced at various residues (Thr-11, Glu-26, Asp-30, Glu-42, Glu-82, Arg-85, Asp-144, Arg-154, Asp-161, Ser-163), including apparently conserved hydrophilic ones. The resulting mutants had essentially the same phenotypes as the wild type, indicating that these residues do not have any significant functional role(s). Analysis of mutations (Gly-150----Asp, Pro, or Ala) indicated that Gly-150 itself was not essential, but that the mutations might affect the structure of the subunit. These results suggest that the overall structure of the delta subunit is necessary, but that individual residues may not have strict functional roles. 相似文献