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排序方式: 共有7186条查询结果,搜索用时 45 毫秒
1.
红曲色素抑菌作用的研究   总被引:28,自引:0,他引:28  
探讨了红曲色素对细菌、放线菌、酵母、霉菌的抑制作用,实验证明,红曲色素对枯草芽孢杆菌、金黄色葡萄球菌具有较强的抑制作用,对大肠杆菌、灰色链霉菌的抑制作用较弱,而对酵母、霉菌、黄色八叠球菌无抑制作用。  相似文献
2.
配施饼肥对烤烟叶片含氮化合物代谢及酶活性的影响   总被引:17,自引:0,他引:17  
通过饼肥用量盆栽试验,研究了K326中部叶在不同生育时期硝酸还原酶和中上部叶片含氮化合物总氮、烟碱、可溶性蛋白质和游离氨基酸含量的变化规律.结果表明,硝酸还原酶随着有机肥施用量的增加酶活性呈增加趋势,中上部叶片的总氮和烟碱含量随有机肥的增加呈上升的趋势,而蛋白质含量则呈下降的趋势,有机肥可以促进游离氨基酸含量的提高.  相似文献
3.
大豆蛋白质纤维的结构研究(Ⅱ):聚集态结构   总被引:14,自引:4,他引:10       下载免费PDF全文
 对大豆蛋白质纤维 (PVA-SPF)的聚集态结构进行了研究 ,认为聚乙烯大分子呈平面锯齿形构象 ,而大豆蛋白大分子在纺丝前的处理过程中已经变性 ,由α-螺旋转变为直线形的 β-链构象 ,并共同砌入纤维 ;由于二组分大分子均带有较多的极性基团 ,在大分子之间可能形成多种键合 ,同时PVA-SPF成纤后进行的缩醛化处理在二组分大分子之间形成了化学交联 ,故而可以认为PVA-SPF的聚集态结构是以直链形大分子网状结构为主体的聚集态结构。X-射线衍射图表明 ,PVA-SPF大分子的结晶能力较弱 ,二维空间排列有序的向列结晶能力较强。  相似文献
4.
在贵州烤烟上发现由棒孢霉属病菌引起的叶斑病   总被引:14,自引:2,他引:12  
1998 ̄1999年在贵州3个县烤烟上发现一种叶斑病,病原真菌鉴定为半知菌类的丛梗孢目、暗梗孢科多胞亚科,棒孢霉属。  相似文献
5.
Tagging of genes by chromosomal integration of PCR amplified cassettes is a widely used and fast method to label proteins in vivo in the yeast Saccharomyces cerevisiae. This strategy directs the amplified tags to the desired chromosomal loci due to flanking homologous sequences provided by the PCR-primers, thus enabling the selective introduction of any sequence at any place of a gene, e.g. for the generation of C-terminal tagged genes or for the exchange of the promoter and N-terminal tagging of a gene. To make this method most powerful we constructed a series of 76 novel cassettes, containing a broad variety of C-terminal epitope tags as well as nine different promoter substitutions in combination with N-terminal tags. Furthermore, new selection markers have been introduced. The tags include the so far brightest and most yeast-optimized version of the red fluorescent protein, called RedStar2, as well as all other commonly used fluorescent proteins and tags used for the detection and purification of proteins and protein complexes. Using the provided cassettes for N- and C-terminal gene tagging or for deletion of any given gene, a set of only four primers is required, which makes this method very cost-effective and reproducible. This new toolbox should help to speed up the analysis of gene function in yeast, on the level of single genes, as well as in systematic approaches.  相似文献
6.
Passive air samplers were used to investigate urban-rural differences of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) over an integrated time period. Samplers consisting of polyurethane foam (PUF) disks and semi-permeable membrane devices (SPMDs) were housed in protective chambers and deployed at six sites for a 4 month duration in the summer of 2000. The sampling transect originated in downtown Toronto and extended approximately 75 km northward into a rural region. Results for the two types of samplers agreed well with one another. Higher blank levels were encountered for the SPMDs, especially for the OCPs, whereas blanks were very low for the PUF disks. Passive sampler-derived air concentrations were consistent with previous measurements of PCBs and OCPs in the region. The largest urban-rural gradient was observed for PCBs (approximately 5-10 times). Chlordanes also showed an urban-rural gradient, possibly reflecting past usage of chlordane on residential lawns and emissions from treated house foundations. Other OCPs exhibited a rural-urban gradient (dieldrin, endosulfan 1, and DDT isomers), which was attributed either to off-gassing from previously treated agricultural soils (dieldrin and DDTs) or to continued usage in agriculture (endosulfan 1). The results of this study demonstrated the feasibility of using such devices to determine air concentrations of persistent organic pollutants (POPs) and to assess their spatial distribution for time-integrated samples. Data such as this is essential for: model validation and for process research and addressing international monitoring strategies on POPs.  相似文献
7.
Delayed Luminescence as an Indicator of Tomato Fruit Quality   总被引:11,自引:0,他引:11  
To develop nondestructructive, objective, quality indicators for tomatoes we measured delayed luminescence, firmness, soluble solids, dry matter, color and respiration during ripening in cherry tomatoes ( Lycopersicon esculentum var. cerasiforme ). They were harvested at various maturity stages and ripened in the dark at 20°C and 80% relative humidity. Ten days after harvest we observed on fruit showing similar color, significant differences in the delayed luminescence, soluble solids and dry matter, directly related to harvest maturity. We suggest that delayed luminescence can be used as a nondestructive indicator of important indicators of tomato fruit quality.  相似文献
8.
Inactivation of microbes using ultrasound: a review   总被引:11,自引:0,他引:11  
Alternative methods for pasteurization and sterilization are gaining importance, due to increased consumer demand for new methods of food processing that have a reduced impact on nutritional content and overall food quality. Ultrasound processing or sonication is one of the alternative technologies that has shown promise in the food industry. Sonication alone is not very effective in killing bacteria in food; however, the use of ultrasound coupled with pressure and/or heat is promising. Thermosonic (heat plus sonication), manosonic (pressure plus sonication), and manothermosonic (heat and pressure plus sonication) treatments are likely the best methods to inactivate microbes, as they are more energy-efficient and effective in killing microorganisms. Ultrasonic processing is still in its infancy and requires a great deal of future research in order to develop the technology on an industrial scale, and to more fully elucidate the effect of ultrasound on the properties of foods.  相似文献
9.
Dialkyl phthalate esters (DPEs) are widely used chemicals, with over 4 million tonnes being produced worldwide each year. On the basis of their octanol-water partition coefficients (Kow), which range from 10(1.61) for dimethyl phthalate to 10(9.46) for di-iso-decyl phthalate, certain phthalate esters have the potential to bioconcentrate and biomagnify in aquatic food webs. However, there are no reported field studies on the trophodynamics of phthalate ester in aquatic food webs. This study reports the distribution of 8 individual phthalate esters (i.e., dimethyl, diethyl, di-isobutyl, di-n-butyl, butylbenzyl, di(2-ethylhexyl), di-n-octyl, and di-n-nonyl) and 5 commercial isomeric mixtures (i.e., di-iso-hexyl (C6), di-iso-heptyl (C7), di-iso-octyl (C8), di-iso-nonyl (C9), and di-iso-decyl (C10)) in a marine aquatic food web. DPE concentrations were determined in 18 marine species, representing approximately 4 trophic levels. Co-analysis of DPEs and 6 PCB congeners (i.e., PCB-18, 99, 118, 180, 194, and 209) in all samples produced a direct comparison of the bioaccumulation behavior of PCBs and DPEs. Lipid equivalent concentrations of the PCBs increased with increasing trophic position and stable isotope ratios (delta15N). The Food-Web Magnification Factor (FWMF) of the PCB congeners ranged from 1.8 to 9.5. Lipid equivalent concentrations of low and intermediate molecular weight DPEs (i.e., C1-C7 DPEs: dimethyl, diethyl, di-iso-butyl, di-n-butyl, benzylbutyl, and C6 and C7 isomers) did not exhibit statistically significant trends with trophic position or stable nitrogen isotope ratios (delta15N) in the food web and FWMFs were not significantly different from 1. Lipid equivalent concentrations of the high-molecular-weight DPEs (i.e., C8-C10 DPEs: di(2-ethylhexyl), di-n-octyl, di-n-nonyl, C8, C9, and C10) declined significantly with increasing trophic position and stable isotope ratios (delta15N), producing FWMFs between 0.25 and 0.48. These results show that all DPEs tested did not biomagnify in the studied aquatic food web whereas PCBs did biomagnify.  相似文献
10.
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