全文获取类型
收费全文 | 7915篇 |
免费 | 769篇 |
国内免费 | 6篇 |
出版年
2022年 | 45篇 |
2021年 | 78篇 |
2020年 | 56篇 |
2019年 | 82篇 |
2018年 | 97篇 |
2017年 | 101篇 |
2016年 | 155篇 |
2015年 | 286篇 |
2014年 | 291篇 |
2013年 | 397篇 |
2012年 | 539篇 |
2011年 | 512篇 |
2010年 | 322篇 |
2009年 | 316篇 |
2008年 | 504篇 |
2007年 | 514篇 |
2006年 | 461篇 |
2005年 | 476篇 |
2004年 | 452篇 |
2003年 | 431篇 |
2002年 | 350篇 |
2001年 | 86篇 |
2000年 | 73篇 |
1999年 | 86篇 |
1998年 | 108篇 |
1997年 | 89篇 |
1996年 | 86篇 |
1995年 | 74篇 |
1994年 | 58篇 |
1993年 | 70篇 |
1992年 | 75篇 |
1991年 | 58篇 |
1990年 | 60篇 |
1989年 | 67篇 |
1988年 | 65篇 |
1987年 | 54篇 |
1986年 | 46篇 |
1985年 | 56篇 |
1984年 | 62篇 |
1983年 | 59篇 |
1982年 | 64篇 |
1981年 | 59篇 |
1980年 | 63篇 |
1979年 | 55篇 |
1978年 | 42篇 |
1977年 | 37篇 |
1976年 | 41篇 |
1975年 | 39篇 |
1974年 | 58篇 |
1973年 | 43篇 |
排序方式: 共有8690条查询结果,搜索用时 343 毫秒
151.
Cyanide-sensitive O2 uptake was observed in the isolated embryonicaxis of soybean [Glycine max L. merr. cv. Essex]within 5 min after wetting and the O2 uptake rate during thefirst h of imbibition was directly proportional to axis moisturecontent. Within 10 min after wetting, O2 uptake was lower inaged low vigor (LV) axes than in high vigor (HV) axes imbibedeither in water (LV axes sustain imbibition injury) or in 30%w/v polyethylene glycol (LV axes do not sustain imbibition injury).Mitochondria isolated from LV axes after 4- and 24-h imbibitionwere characterized by lower O2 uptake, ADP:O, and respiratorycontrol ratios relative to HV mitochondria. A plot of O2 uptakevs temperature between 10 and 25?C revealed a break in the slopebetween 13 and 16?C for HV, but not LV, axes. Since LV axessustained water uptake injury at all temperatures tested, whereasHV axes sustained chilling injury only below 16?C, the dataindicate two temperature-O2 uptake relationships: one for injuredtissues and one for non-injured tissues. We conclude that deteriorationper se involves impairment of respiratory metabolism in thesoybean embryonic axis. Chilling (10?C; HV and LV axes) andimbibitional (25?C; LV axes) injuries during the initial minof inbibition further disrupt respiratory metabolism and interferewith subsequent mitochondrial development and axis growth.
1Scientific Articles No. A-3548, Contribution No. 6623 of theMaryland Agricultural Experiment Station. (Received May 25, 1983; Accepted September 28, 1983) 相似文献
152.
153.
Pravit Cadnapaphornchai Gary Aisenbrey Keith M. McDonald Thomas J. Burke Robert W. Schrier 《Prostaglandins & other lipid mediators》1978,16(6):965-971
Acute elevation of ureteral pressure to 100 mm Hg in anesthetized dogs (n=7) resulted in an increase (P<0.005) in systemic blood pressure from 151±7 to 163 ± 7 mm Hg, a transient (15 min) increase (P<0.05) in renal blood flow from 413 ± 27 to 465 ± 27 ml/min C and a rise (P<0.05) in plasma renin activity from 6.0 ± 1.6 to 10.3 ± 2.1 ng/ml/hr. Pretreatment with a competitive inhibitor of angiotensin II, i.e. sar1gly8AII, abolished the hypertensive response to acute ureteral obstruction, and pretreatment with 2 mg/kg of either indomethacin (n=6) or meclofenamate (n=3), 15 min before obstruction, prevented the hyperemic response. These results suggest that acute ureteral obstruction leads to hypertension via activation of the renin-angiotensin system and hyperemia via a prostaglandin-initiated mechanism. 相似文献
154.
The 10,000-nucleotide RNA genome of the Prague strain, subgroup B (PR-B) of Rous sarcoma virus, was found to contain 11.6 ± 0.5 residues of m6Ap by quantitative analysis of 32P-labeled virion RNA after complete RNAase digestion. Approximately ten of the m6Ap residues are located, without obvious clustering, in that region of the genome between 500 and 4000 nucleotides from the 3′ poly(A) end. The src gene, which is required for transformation, and part of the env gene, which codes for the major viral envelope glycoprotein, have previously been mapped in this region of the viral genome. A transformation-defective deletion mutant of PR-B Rous sarcoma virus, which lacks the src gene, has 7.0 ± 0.2 m6Ap residues per RNA subunit. This supports our mapping of a portion of the m6A residues in src and suggests that this methylation is specific to certain regions of the genome. The possible significance of this result for Rous sarcoma virus RNA processing and translation is discussed. 相似文献
155.
Line broadening of spin label signals is treated in terms of concentration, viscosity, charge and temperature dependencies. Line broadening of spin label signals may be caused either by spin label interactions or by the interaction between a spin label and a second paramagnetic species. Line broadening has been related to collision frequency in the literature and is treated in that way here. Collision frequency is related to diffusion processes in a way that allows information to be obtained about the diffusion environment. Several potential spin label line-broadening agents are compared as to their effectiveness. Small polymer beads with graduated pore sizes are used to show that collisional broadening has a marked dependence on the long-range structure of the diffusion environment. Application of these results to biological diffusion processes is considered. 相似文献
156.
Guanosine 5′-triphosphate and guanosine 5′-[βγ-imido]triphosphate effect a collision coupling mechanism between the glucagon receptor and catalytic unit of adenylate cyclase 总被引:7,自引:6,他引:1
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1. GTP, but not p[NH]ppG (guanosine 5′-[βγ-imido]triphosphate), abolishes the sensitivity of glucagon-stimulated adenylate cyclase to the lipid-phase separations occurring in the outer half of the bilayer in liver plasma membranes from rat. 2. When either GTP or p[NH]ppG alone stimulate adenylate cyclase, the enzyme senses only those lipid-phase separations occurring in the inner half of the bilayer. 3. Trypsin treatment of intact hepatocytes has no effect on the basal, fluoride-, GTP- or p[NH]ppG-stimulated adenylate cyclase activity. However, 125I-labelled-glucagon specific binding decays with a half-life matching that of the decay of glucagon-stimulated adenylate cyclase activity. 4. When GTP or p[NH]ppG are added to assays of glucagon-stimulated activity, the half-life of the trypsin-mediated decay of activity is substantially increased and the decay plots are no longer first-order. 5. Trypsin treatment of purified rat liver plasma membranes abolishes basal and all ligand-stimulated adenylate cyclase activity, and 125I-labelled-glucagon specific binding. 6. Benzyl alcohol activates the GTP- and p[NH]ppG-stimulated activities in an identical fashion, whereas these activities are affected differently when glucagon is present in the assays. 7. We suggest that guanine nucleotides alter the mode of coupling between the receptor and catalytic unit. In the presence of glucagon and GTP, a complex of receptor, catalytic unit and nucleotide regulatory protein occurs as a transient intermediate, releasing a free unstable active catalytic unit. In the presence of p[NH]ppG and glucagon, the transient complex yields a relatively stable complex of the catalytic unit associated with a p[NH]ppG-bound nucleotide-regulatory protein. 相似文献
157.
Total RNA was extracted from fast growing suspension cells of bean, the mRNA was translated and the products of protein synthesis analysed by gel electrophoresis. Actinomycin D (20 g ml–1) added to the cultures 12 h before the induction of phenylalanine ammonia-lyase (PAL) activity by naphthylacetic acid (NAA) (1 mg/l) and kinetin (0.2 mg/l) failed to prevent the increased activity of the enzyme usually produced by this ratio of the plant growth hormones. PAL was isolated and purified from suspension cultured bean cells. The purified enzyme ran as a single band on polyacrylamide gel electrophoresis. The protein translated from RNA prepared from induced and non-induced cells was separated by gel electrophoresis and the bands of protein on the gels were compared. There was no evidence for an increase in the amount of PAL synthesised in vitro from the mRNA of induced cells even though these had 5 times the amount of activity of the enzyme compared with that of the non-induced cells. The results indicate that the induction of PAL activity is not immediately preceeded by an increase in the synthesis of PAL-mRNA by the cells. The control of the activity of the enzyme is discussed with respect to this finding.Abbreviations PAL
phenylalanine ammonia-lyase
- NAA
3naphthylacetic acid
- DEAE
Diethylamino ethyl
- EDTA
Ethylenediamine tetraacetate
- SDS
Sodium dodecyl sulphate 相似文献
158.
Metal tolerance in tissue cultures of anthoxanthum odoratum 总被引:1,自引:0,他引:1
Javed A. Qureshi Hamish A. Collin Keith Hardwick David A. Thurman 《Plant cell reports》1981,1(2):80-82
Tissue cultures were initiated from one non-tolerant (S20) and two zinc and lead tolerant (T92 and T94) clones of Anthoxanthum odoratum. Growth of callus from the non-tolerant clone was reduced by the presence of zinc, lead, copper and nickel, whereas callus from the two tolerant clones showed no reduction of growth in the presence of zinc and lead but growth was reduced by copper and nickel. The specificity of metal tolerance shown by the parental material was maintained in the callus. Tolerant and non-tolerant callus accumulated similar amounts of zinc and lead. 相似文献
159.
It is shown that the time-course of incorporation of radioactivity from [3-14C]serine into nucleic acids parallels DNA synthesis following mitogenic stimulation of human peripheral blood lymphocytes by phytohaemagglutinin (PHA). The activity of serine hydroxymethyltransferase was elevated about four-fold in PHA-stimulated lymphocytes compared to that in unstimulated control ceils. It is suggested that lymphocytes, in common with other proliferating cell systems:, may synthesize serine de novo for utilization in pathways of nucleotide biosynthesis following mitogenic stim--ulation. 相似文献
160.
H. Keith Massel Salvador Macias Darlene M. Meador Duane M. Rumbaugh 《International journal of primatology》1981,2(1):9-17
Twenty-month-old rhesus monkeys were tested in a modified discrimination-reversal paradigm, which was designed to distinguish
abstract learning from stimulus-response associational learning. Previous studies indicate that talapoin monkeys learn associationally
and great apes via forming abstract concepts. Adult rhesus monkeys are apparently capable of forming simple abstractions,
but learn primarily through associational process. The results of this study show the adolescent rhesus monkeys to be associational
learners, with their response patterns indicating more complexity than the talapoins but less than the adult rhesus monkeys.
The data suggest that rhesus monkeys develop their low-level capacity of abstract learning with maturation. 相似文献