全文获取类型
收费全文 | 6159篇 |
免费 | 548篇 |
国内免费 | 334篇 |
出版年
2024年 | 18篇 |
2023年 | 207篇 |
2022年 | 295篇 |
2021年 | 329篇 |
2020年 | 298篇 |
2019年 | 359篇 |
2018年 | 338篇 |
2017年 | 278篇 |
2016年 | 224篇 |
2015年 | 238篇 |
2014年 | 363篇 |
2013年 | 398篇 |
2012年 | 255篇 |
2011年 | 359篇 |
2010年 | 240篇 |
2009年 | 259篇 |
2008年 | 287篇 |
2007年 | 269篇 |
2006年 | 245篇 |
2005年 | 223篇 |
2004年 | 201篇 |
2003年 | 189篇 |
2002年 | 135篇 |
2001年 | 78篇 |
2000年 | 91篇 |
1999年 | 70篇 |
1998年 | 54篇 |
1997年 | 55篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 35篇 |
1984年 | 53篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 46篇 |
1980年 | 32篇 |
1979年 | 36篇 |
1978年 | 43篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1975年 | 18篇 |
1974年 | 22篇 |
排序方式: 共有7041条查询结果,搜索用时 15 毫秒
91.
A case of somatic instability affecting aleurone colour in a strain of maize from India with flint background was analysed.
The somatic instability is localized to theC
1 (Inhibitor) allele ofC locus on the short arm of chromosome 9. Molecular tests indicated thatAc is not present in the Indian stock and the evidence is consistent with the involvement of theEn (Spm) transposable element in the instability. The presence of theEn (Spm)-like element in the stock would suggest that these elements have been present in the maize genome for a long time. A new
allele ofshrunken (sh1) gene with a somewhat unorthodox breeding behaviour is also described. 相似文献
92.
Interaction of a spin-labeled 9-aminoacridine with DNA was studied by electron spin resonance spectroscopy. Accurate determination of the binding parameters, equilibrium dissociation constant (KD), and total number of ligand-binding sites was obtained using Scatchard and Lineweaver-Burk plots. The competition between 9-aminoacridine and its spin-labeled derivative was examined by a similar analysis of the spin-label signals. The practical interest of this method lies in the fact that the precision and the simplicity of the measurements allow the quantitative determination of the binding capacity of any intercalative drug which interacts specifically with adenine/thymine bases of DNA. 相似文献
93.
The genetic effects of MNNG, 4NQO and ICR-170 have been compared on 5 different UV-sensitive strains and a standard wild-type strain of Neurospora crassa with regard to inactivation and the induction of forward-mutations at the ad-3A and ad-3B loci. Whereas all UV-sensitive strains (upr-1, uvs-2, uvs-3, uvs-5 and uvs-6) are more sensitive to inactivation by MNNG and ICR-170 than wild-type, only uvs-5 shows survival comparable to wild-type after 4NQO treatment, all other strains are more sensitive to 4NQO. In contrast to the effects on inactivation, a wide variety of effects were found for the induction of ad-3A and ad-3B mutations: higher forward-mutation frequencies than were found in wild-type were obtained after treatment with MNNG or 4NQO for upr-1 and uvs-2, no significant increase over the spontaneous mutation frequency was found with uvs-3 after MNNG, 4NQO or ICR-170 treatment; mutation frequencies comparable to that found in wild-type were obtained with uvs-6 after MNNG, 4NQO or ICR-170 treatment and with upr-1 after ICR-170 treatment. Lower forward-mutation frequencies than were found in wild-type were obtained with uvs-2 after ICR-170 treatment and with uvs-5 after MNNG, 4NQO or ICR-170 treatment. These data clearly show that the process of forward-mutation at the ad-3A and ad-3B loci is under genetic control by mutations at other loci (e.g. upr-1, uvs-2, uvs-3, uvs-5 and uvs-6) and that the effect is markedly mutagen-dependent. 相似文献
94.
Steroid acid esters, synthesized by modifying the 17-ketol side chain of prednisolone, were tested for their in vitro ability to stabilize heavy mitochondrial lysosomes prepared from rat liver. Membrane stabilization was determined by assessing capability of steroids to decrease extrusion of the marker enzymes (acid phosphatase, beta-glucuronidase and aryl sulfatase) from lysosomes incubated in hypo-osmotic sucrose-Tris acetate buffer. Results indicated that prednisolone (1) significantly inhibited the lysosomal release of acid phosphatase as did the new anti-inflammatory steroid, methyl 20-dihydroprednisolonate. Methyl prednisolonate exhibited weak membrane stabilization capacities and 20-dihydroprednisolonic acid, a metabolic product of methyl 20-dihydroprednisolonate, showed virtually no membrane stabilization. 相似文献
95.
Robert S.U. Baker Antonio M. Bonin Ieva Stupans Gerald M. Holder 《Mutation research》1980,71(1):43-52
A highly significant enhancement of mutagenicity occurs with 11 polycyclic aromatic hydrocarbons when 3-methylcholanthrene-induced guinea pig liver S9 is substituted for Aroclor-induced rat liver S9 in the Ames test. The use of MC-induced guinea pig liver S9 is particularly valuable for detecting the weak mutagenicity of benz[c]acridine, which is barely positive in a standard Ames assay. However, anthracene and phenanthrene, which are generally considered not to be carcinogens, remain non-mutagenic for strain TA100. This enhancement of mutagenicity does not correlate with arylhydrocarbon hydroxylase activities of the various liver preparations and does not apply to certain other non-PAH mutagens, including β-naphthylamine, aflatoxin B1 and 4-dimethylaminoazobenzene. 相似文献
96.
Asynchronous 9L cells were separated into relatively homogeneously-sized populations using centrifugal elutriation with both
a conventional collection method and a long collection method. A substantial increase in the homogeneity of the volume distributions
and in the degree of synchrony of the separated fractions was obtained using the long collection method. Autoradiographic
data indicated that fractions containing ≥97% G1 cells, ≥80% S cells, and 70–75% G2 cells could be routinely recovered with this procedure. Recovery in these fractions varied from 5 to 8% of the total number
of cells elutriated. The colony forming efficiency (CFE) of cells from fractions representing each phase of the cell cycle
was a constant 60–70%, which was comparable to the 60–80% usually found for asynchronous 9L cells. The percentage of cells
in the G1, S, and G2 phases in the elutriated fractions was more accurately determined from the volume distribution than from computer fits of
the DNA histogram obtained from flow cytometry. In general, the degree of synchrony was related to the coefficient of variation
(CV) of the volume distributions of the elutriated fractions. The CV was about 14% for all elutriated fractions. When the
≥97% G1 population was allowed to progress to S and G2, the CVs were about 17 and 20.2%, respectively. Thus, the best nonperturbing method for obtaining synchronous 9L cells in
the S or G2 phases was direct elutriation with the long collection method. 相似文献
97.
A. Herchuelz P. Lebrun A. Carpinelli N. Thonnart A. Sener W.J. Malaisse 《生物化学与生物物理学报:生物膜》1981,640(1):16-30
The effects of quinine and 9-aminoacridine, two blockers of potassium conductance in islet cells, on 45Ca efflux and insulin release from perifused islets were investigated in order to elucidate the mechanisms by which glucose initially reduces 45Ca efflux and later stimulates calcium inflow in islet cells. In the absence of glucose, 100 μM quinine stimulated 45Ca net uptake, 45Ca outflow rate and insulin release. Quinine also dramatically enhanced the cationic and the secretory response to intermediate concentrations of glucose, but had little effect on 45Ca net uptake, 45Ca fractional outflow rate and insulin release at a high glucose concentration (16.7 mM). The ability of quinine to stimulate 45Ca efflux depended on the presence of extracellular calcium, suggesting that it reflects a stimulation of calcium entry in the islet cells. In the absence of extracellular calcium, quinine provoked a sustained decrease in 45Ca efflux. Such an inhibitory effect was not additive to that of glucose, and was reduced at low extracellular Na+ concentration. At a low concentration (5 μM), quinine, although reducing 86Rb efflux from the islets to the same extent as a non-insulinotropic glucose concentration (4.4 mM), failed to inhibit 45Ca efflux. In the presence of extracellular calcium, 9-aminoacridine produced an important but transient increase in 45Ca outflow rate and insulin release from islets perifused in the absence of glucose. In the absence of extracellular calcium, 9-aminoacridine, however, failed to reduced 45Ca efflux from perifused islets. It is concluded that quinine, by reducing K+ conductance, reproduces the effect of glucose to activate voltage-sensitive calcium channels and to stimulate the entry of calcium into the B-cell. However, the glucose-induced inhibition of calcium outflow rate, which may also participate in the intracellular accumulation of calcium, does not appear to be mediated by changes in K+ conductance. 相似文献
98.
The effect of pre- and posttreatment incubation of UV-irradiated and ethyl methanesulphonate (EMS) treated cells with non-toxic concentrations of inhibitors of de novo purine synthesis (dnPS) on expression of potentially lethal and premutational damage at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus in V79 cells has been examined. The concentrations of inhibitors used were shown to profoundly perturb de novo DNA synthesis, by measurements of [14C]formate uptake, and cell cycle progression by flow cytofluorimetry. Postincubation in 6-methyl mercaptopurine ribonucleoside (MMPR) usually but not invariably potentiated the cytotoxic effects of UV and EMS but azaserine (AZS) and methotrexate (MTX) were without effect. No effects on mutant frequencies were observed on posttreatment with any of these agents. Caffeine produced the least effect on dnPS, but invariably potentiated lethal damage. This potentiation of lethal damage is not mediated by dnPS inhibition as has been suggested for Chinese hamster ovary (CHO) cells. 相似文献
99.
9-Hydroxyellipticine (9-hydroxy-5,11-dimethyl-6-H-pyrido[4,3b]carbazole), a potent inhibitor of monooxygenases, strongly inhibits the initiation of skin tumors by 7,12-dimethylbenz[a]anthracene (DMBA) in male NMRI Swiss mice. 9-Hydroxyellipticine has not effect on promotion step. 相似文献
100.
M. Kehat S. Gothilf E. Dunkelblum S. Greenberg 《Entomologia Experimentalis et Applicata》1980,27(2):188-193
(Z)-11-hexadecenal and (Z)-9-hexadecenal were ineffective lures forH. armigera males unless combined. Attraction depended upon perception of a 90%–99% combination of (Z)-11-hexadecenal with 1%–10% (Z)-9-hexadecenal. Increasing the level of (Z)-9-hexadecenal in the mixture to 26.2% reduced catches. Adding 2.3% (Z)-7-hexadecenal to the mixture did not enhance or reduce attraction, while adding 8.7% (Z)-11-hexadecenol significantly reduced male catches. The combination of (Z)-11-hexadecenal and (Z)-9-hexadecenal was effective only when released from rubber dispensers but not from polyethylene vials. A load of 2 mg of the mixture on rubber dispensers effectively attracted males for at least 31 days. TheH. zea lure which contained all the pheromonal components of that species was also effective in attractingH. armigera males. TheH. virescens lure attracted significantly fewerH. armigera males than theH. zea lure.
Résumé Les (Z)-11-hexadecenal et (Z)-9-hexadecenal sont des attractifs sexuels in efficaces pour les mâles deH. armigera. L'attraction dépend de la perception d'un mélange de 90 à 99% de (Z)-11-hexadecenal avec 1 à 10% (Z)-9-hexadecenal, L'augmentation jusqu'à 26,2% de la teneur en (Z)-9-hexadecenal réduit les captures. L'addition de 2,3% de (Z)-7-hexadecenal au mélange ne modifie pas l'attractivité, tandis que celle de 8,7% de (Z)-11-hexadecenol, réduit significativement les captures de mâles. Le mêlange de (Z)-11-hexadecenal et de (Z)-9-hexadecenal n'a été efficace qu'avec des diffuseurs en caoutchouc, par contre il a été sans effet à partir de récipients de polyéthylène. Une charge de 2 mg de mélange dans des diffuseurs en caoutchouc attire effectivement les mâles pendant ou moins 31 jours. L'attractif sexuel deH. zea qui contient tous les constituants de la phéromone de cette espèce attire aussi efficacement les mâles deH. armigera. Celui deH. virescens attire significativement moins de mâles deH. armigera que l'attractif sexuel deH. zea.相似文献