全文获取类型
收费全文 | 5731篇 |
免费 | 371篇 |
出版年
2023年 | 20篇 |
2022年 | 26篇 |
2021年 | 60篇 |
2020年 | 43篇 |
2019年 | 40篇 |
2018年 | 93篇 |
2017年 | 99篇 |
2016年 | 156篇 |
2015年 | 285篇 |
2014年 | 293篇 |
2013年 | 383篇 |
2012年 | 462篇 |
2011年 | 406篇 |
2010年 | 242篇 |
2009年 | 195篇 |
2008年 | 344篇 |
2007年 | 345篇 |
2006年 | 297篇 |
2005年 | 271篇 |
2004年 | 244篇 |
2003年 | 243篇 |
2002年 | 259篇 |
2001年 | 92篇 |
2000年 | 95篇 |
1999年 | 73篇 |
1998年 | 43篇 |
1997年 | 29篇 |
1996年 | 28篇 |
1995年 | 33篇 |
1994年 | 37篇 |
1993年 | 31篇 |
1992年 | 48篇 |
1991年 | 54篇 |
1990年 | 53篇 |
1989年 | 46篇 |
1988年 | 41篇 |
1987年 | 54篇 |
1986年 | 35篇 |
1985年 | 43篇 |
1984年 | 51篇 |
1983年 | 33篇 |
1982年 | 21篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 24篇 |
1974年 | 22篇 |
1973年 | 36篇 |
1972年 | 24篇 |
1971年 | 23篇 |
排序方式: 共有6102条查询结果,搜索用时 16 毫秒
81.
Biosynthesis of alginate in algae may be studied by following the cell wall regeneration of brown seaweed protoplasts in culture. The enzyme mannuronan C-5 epimerase will control the composition of the alginate being synthetized.Freshly isolated protoplasts from the thallus of young Laminaria digitata plants showed only low expression of this enzyme. However, after prolonged periods in culture, this activity increased 15-fold. The synthesis of C-5 epimerase by the protoplasts is probably essential for the formation of a new cell wall.After cellular disruption by osmotic shock and centrifugation, most of the epimerase activity resided in the pellet fraction. This may indicate that the enzyme is membrane associated. 相似文献
82.
Immunoaffinity co-purification of cytokinins and analysis by high-performance liquid chromatography with ultraviolet-spectrum detection 总被引:1,自引:0,他引:1
A rapid methodology for the simultaneous analysis of a large number of cytokinins is presented. The cross-reactivity of a mixture of polyclonal antibodies against zeatin riboside and isopentenyladenosine was exploited in a protocol that can be used for immunoaffinity purification of 23 additional cytokinins. Ligands include the cytokinin bases zeatin, dihydrozeatin, isopentenyladenine, benzyl-adenine and kinetin, and their corresponding nucleoside, nucleoside-5′-monophosphate, and 9-glucoside derivatives, as well as cis-zeatin, cis-zeatin riboside, the 2-methylthiol derivatives of isopentenyladenosine and zeatin riboside, and benzyl-adenine-3-glucoside. Mixtures of cytokinins could be retained with high recoveries of all the components. Immunoaffinity purification of extracts of Arabidopsis thaliana (L.) Heynh. and Solarium tuberosum L. gave fractions clean enough, as verified by gas chromatographymass spectrometry (GC-MS), to allow analysis of endogenous cytokinins using a single high-performance liquid chromatography (HPLC) step with on-line UV-spectrum detection. The detection limit was 4–6 pmol. The procedure described forms a routine assaying technique that is faster and simpler, yet yields better qualitative and quantitative information than the commonly used procedure of immunoassaying of HPLC fractions. 相似文献
83.
Bjørn-Yngvar Nordvåg Ida Ranløv Hilde Monica Frostad Riise Gunnar Husby M. Raafat El-Gewely 《Human genetics》1993,92(3):265-268
Severe familial amyloid cardiomyopathy (FAC) in a Danish kindred is associated with a specific mutation (Met for Leu 111) in the transthyretin (TTR) gene. The mutation causes the loss of a DdeI restriction site in the gene, allowing molecular diagnostic studies. We studied formalin-fixed, paraffin-embedded tissues, up to 39 years old, from 29 family members of this kindred. DNA was partially purified from deparaffinized tissue sections and a DNA sequence of the TTR gene flanking the mutation site was amplified by the polymerase chain reaction (PCR), followed by restriction enzyme analysis. Amplified DNA was obtained from tissues representing 23 of the 29 persons. Ten out of the 23 family members were found to carry the TTR Met 111 mutation, whereas 13 were not affected. The results were consistent with known clinical data and with corresponding serum TTR examinations. This retrospective study shows that archival tissues can be used to confirm the diagnosis and disease pattern in members of families affected by hereditary diseases. 相似文献
84.
Terje Kalland Mikael Dohlsten Lars Abrahmsén Gunnar Hedlund Per Björk Peter A. Lando Anette Sundstedt Eva Åkerblom Peter Lind 《Cell biochemistry and biophysics》1993,22(1-3):147-164
The bacterial superantigen staphylococcal enterotoxin A (SEA) is an extremely potent activator of T lymphocytes when presented on MHC class II antigens. In order to induce T lymphocytes to reject a tumor, we substituted the specificity of SEA for MHC class II molecules with specificity for tumor cells by combining SEA with a MAb recognizing colon carcinomas. Chemical conjugates or recombinant fusion proteins of the MAb C215 and SEA retained excellent antigen binding properties whereas the binding to MHC class II was markedly reduced. The hybrid proteins directed SEA responsive T cells to tumors with specificity determined by the specificity of the MAb. Significant tumor cell killing was obtained at picomolar concentrations of the hybrid proteins and was the result of direct cell mediated by cytotoxicity as well as production of tumoricidal cytokines by T cells. Targeting of superantigens represents a novel approach to specific immunomodulation and deserves further study as a potential therapy for malignant disease. 相似文献
85.
Transformation of pecan and regeneration of transgenic plants 总被引:5,自引:0,他引:5
Gale H. McGranahan Charles A. Leslie Abhaya M. Dandekar Sandra L. Uratsu Ida E. Yates 《Plant cell reports》1993,12(11):634-638
A gene transfer system developed for walnut (Juglans regia L.) was successfully applied to pecan (Carya illinoensis [Wang] K. Koch). Repetitively embryogenic somatic embryos derived from open-pollinated seed of Elliott, Wichita, and Schley were co-cultivated with Agrobacterium strain EHA 101/pCGN 7001, which contains marker genes for beta-glucuronidase activity and resistance to kanamycin. Several modifications of the standard walnut transformation techniques were tested, including a lower concentration of kanamycin and a modified induction medium, but these treatments had no measurable effect on efficiency of transformation. Nineteen of the 764 viable inoculated embryos produced transgenic subclones; 13 of these were from the line Elliott6, 3 from Schley5/3, and 3 from Wichita9. Transgenic embryos of Wichita9 germinated most readily and three subclones were successfully micropropagated. Three transgenic plants of one of these subclones were obtained by grafting the tissue cultured shoots to seedling pecan rootstock in the greenhouse. Gene insertion, initially detected by GUS activity, was confirmed by detection of integrated T-DNA sequences using Southern analysis. 相似文献
86.
C. Olivari Maria Chiara Pugliarello Franca Rasi-Caldogno Maria Ida De Michelis 《Plant biology (Stuttgart, Germany)》1993,106(1):13-19
The aqueous two-phase partitioning technique was utilized to isolate a plasma membrane (PM) fraction from etiolated seedlings of Arabidopsis thaliana. The purification procedure adopted yielded a fraction highly enriched in PM as compared to inner membranes, with a recovery of about 30%, as judged from the activities of PM markers such as vanadate-sensitive ATPase, FC binding and UDP-glucose sterol glucosyltransferase. The purified PM fraction displayed vanadate-sensitive H+ pumping activity. Its purity was confirmed by the biochemical characteristics of its ATPase activity assayed in the absence of Ca2+: sensitivity to vanadate (IC50 ca. 1 μM), Mg2+-dependence, insensitivity to molybdate, oligomycin and nitrate, pH optimum at 6.6. The PM H+-ATPase activity was stimulated by fusicoccin and by a controlled treatment of the PM with trypsin. In both cases stimulation was much stronger on the activity assayed at pH 7.5 than on the activity at pH 6.6. Moreover, neither fusicoccin nor the treatment with trypsin stimulated the portion of activity (30 to 40% at pH 7.5) which decayed upon preincubation of the PM in assay medium without ATP. 相似文献
87.
88.
Thomas Schiewe Björn Gutschmann Lara Santolin Saskia Waldburger Peter Neubauer Roland Hass Sebastian L. Riedel 《Biotechnology and bioengineering》2023,120(10):2880-2889
An efficient monitoring and control strategy is the basis for a reliable production process. Conventional optical density (OD) measurements involve superpositions of light absorption and scattering, and the results are only given in arbitrary units. In contrast, photon density wave (PDW) spectroscopy is a dilution-free method that allows independent quantification of both effects with defined units. For the first time, PDW spectroscopy was evaluated as a novel optical process analytical technology tool for real-time monitoring of biomass formation in Escherichia coli high-cell-density fed-batch cultivations. Inline PDW measurements were compared to a commercially available inline turbidity probe and with offline measurements of OD and cell dry weight (CDW). An accurate correlation of the reduced PDW scattering coefficient µs′ with CDW was observed in the range of 5–69 g L−1 (R2 = 0.98). The growth rates calculated based on µs′ were comparable to the rates determined with all reference methods. Furthermore, quantification of the reduced PDW scattering coefficient µs′ as a function of the absorption coefficient µa allowed direct detection of unintended process trends caused by overfeeding and subsequent acetate accumulation. Inline PDW spectroscopy can contribute to more robust bioprocess monitoring and consequently improved process performance. 相似文献
89.
Transformation of Arabidopsis thaliana with the codA gene for choline oxidase; accumulation of glycinebetaine and enhanced tolerance to salt and cold stress 总被引:12,自引:0,他引:12
Hidenori Hayashi Alia Laszlo Mustardy Patchraporn Deshnium Miki Ida Norio Murata 《The Plant journal : for cell and molecular biology》1997,12(1):133-142
Glycinebetaine is one of the compatible solutes that accumulate in the chloroplasts of certain halotolerant plants when these plants are exposed to salt or cold stress. The codA gene for choline oxidase, the enzyme that converts choline into glycinebetaine, has previously been cloned from a soil bacterium, Arthrobacter globiformis. Transformation of Arabidopsis thaliana with the cloned codA gene under the control of the 35S promoter of cauliflower mosaic virus enabled the plant to accumulate glycinebetaine and enhanced its tolerance to salt and cold stress. At 300 mM NaCl, considerable proportions of seeds of transformed plants germinated well, whereas seeds of wild-type plants failed to germinate. At 100 mM NaCl, transformed plants grew well whereas wild-type plants did not do so. The transformed plants tolerated 200 mM NaCl, which was lethal to wild-type plants. After plants had been incubated with 400 mM NaCl for two days, the photosystem II activity of wild-type plants had almost completely disappeared, whereas that of transformed plants remained at more than 50% of the original level. When exposed to a low temperature in the light, leaves of wild-type plants exhibited symptoms of chlorosis, whereas those of transformed plants did not. These observations demonstrate that the genetic modification of Arabidopsis thaliana that allowed it to accumulate glycinebetaine enhanced its ability to tolerate salt and cold stress. 相似文献
90.
Migraine is the most common neurological disorder, affecting about 20% of adults. The mode of inheritance was analyzed in the two main types of migraine, migraine without aura (MO) and migraine with aura (MA), by complex segregation analysis using the computer program POINTER. We included 126 probands with MO and 127 probands with MA from the general population. Firstdegree relatives and spouses were blindly interviewed by a neurological research fellow. The complex segregation analysis indicated that both MO and MA have multifactorial inheritance without generational difference. 相似文献