首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   289篇
  免费   13篇
  2023年   1篇
  2022年   2篇
  2021年   11篇
  2020年   6篇
  2019年   4篇
  2018年   6篇
  2017年   5篇
  2016年   7篇
  2015年   12篇
  2014年   15篇
  2013年   15篇
  2012年   26篇
  2011年   19篇
  2010年   21篇
  2009年   13篇
  2008年   23篇
  2007年   16篇
  2006年   18篇
  2005年   4篇
  2004年   17篇
  2003年   10篇
  2002年   8篇
  2001年   5篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1996年   3篇
  1995年   4篇
  1994年   5篇
  1992年   4篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1982年   2篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1974年   1篇
  1968年   1篇
  1967年   1篇
  1966年   2篇
  1965年   1篇
  1964年   1篇
  1962年   1篇
  1961年   1篇
排序方式: 共有302条查询结果,搜索用时 15 毫秒
41.

Purpose

Many companies around the world have been challenged to make their products in a more sustainable way in the last decade in order to minimize their environmental impacts. Klabin, the largest producer, exporter, and recycler of paper in Brazil, has made great efforts to exchange old for new and more efficient equipment to produce cellulose packaging materials. The objective of this study was to measure the benefits of modernization of its plant located in the southern region of the country for manufacturing carrier board/folding box board (CB/FBB) and kraftliner paper (KP).

Methods

The goal established was analyzed through a cradle-to-gate life cycle assessment methodology.

Results and discussion

The modernization carried out has led to several improvements such as the reductions measured by the functional units of 1,000 kg of CB/FBB and 1,000 kg of KP, respectively, of energy consumption (21 and 3 %), water (8.5 % for CB/FBB only), wood (6.6 and 7.2 %), and land use (6.9 and 7.1 %). The environmental impact categories (according to CML 2001) that have suffered greater reductions are human toxicity (68 and 69 %), abiotic depletion (59 and 28 %), and global warming potential (51 and 9 %) for the same reference units.

Conclusions

The results achieved clearly show the importance of renewing industrial plant in order to achieve better environmental performance and also provide a historical inventory perspective for the company to establish future targets for improvement.  相似文献   
42.
Polymerization of Gag on the inner leaflet of the plasma membrane drives the assembly of Human Immunodeficiency Virus 1 (HIV-1). Gag recruits components of the endosomal sorting complexes required for transport (ESCRT) to facilitate membrane fission and virion release. ESCRT assembly is initiated by recruitment of ALIX and TSG101/ESCRT-I, which bind directly to the viral Gag protein and then recruit the downstream ESCRT-III and VPS4 factors to complete the budding process. In contrast to previous models, we show that ALIX is recruited transiently at the end of Gag assembly, and that most ALIX molecules are recycled into the cytosol as the virus buds, although a subset remains within the virion. Our experiments imply that ALIX is recruited to the neck of the assembling virion and is mostly recycled after virion release.  相似文献   
43.
A series of potent and competitive inhibitors of UDP-glucuronosyltransferase derived from 7,7,7-triphenylheptanoic acid has been synthesized in order to probe the active site of the isozyme involved in the glucuronidation of the endogenous toxic compound, bilirubin IXα. Like triphenylalkylcarboxylic acids, triphenyl alcohols were found to be very effective competitive inhibitors of the reaction (Ki 12 to 180 μM). Superimposition of the best inhibitors with bilirubin by computer modeling showed a marked spatial similarity, which accounts for the observed competitive-type inhibition. The bulky triphenylmethyl moiety of the inhibitor superimposed well on the part of the bilirubin molecule containing three of the four pyrrole rings. In agreement, substitution of the triphenylmethyl moiety by planar structures such as fluorenyl or indenyl rings completely suppressed the inhibition. In addition, the weak inhibition exerted by the shortest carboxylic acids could be related to the higher acidity of these molecules. The inhibition potency depended on the acidity of the molecules; the more acidic, the less inhibitory, suggesting that the presence of a negative charge on the inhibitor molecule prevents bilirubin glucuronidation. Based on these results, a reaction mechanism for bilirubin glucuronidation is postulated. © 1997 John Wiley & Sons, Inc. J Biochem Toxicol 12: 19–27, 1998  相似文献   
44.
Upon immunization of mice with a mAb (290A-167) directed against an epitope of Lol p I (the major allergenic determinant of Lolium perenne), both anti-idiotypic (aId) mAb (Ab2) and anti-aId mAb (Ab3) were produced. The Ab2 displayed the following internal image properties of Lol p I: it can be affinity-purified on an immobilized Id column; its binding to the anti-Lol p I mAb (290A-167) is inhibited by Lol p I; it inhibits in a dose-response fashion the binding of the specific Id to Ag. It is recognized by anti-Lol p I antisera from different species such as mouse, human, and goat. The Ab3 which binds to Lol p I was also produced from the same fusion. This binding was inhibited significantly by aId mAb (Ab2), anti-Lol p I mAb (290A-167) and Lol p I. These data indicate that the two mAb with specificity for Lol p I (290A-167 and Ab3) share similar reactivity to the Ag and that aId mAb is the internal image of the epitope recognized by the Id. We showed also that the capacity of rabbit aId Ab directed against the 290A-167 Id to inhibit the binding of Ab1 and Ab3 to Ag was almost abolished by passage over a Ab3-coated Sepharose column. This would suggest that not only are the two mAb with reactivity to Lol p I (Ab1 and Ab3) directed against identical epitopes, but that they in fact shared identical idiotopes as well. The production of identical mAb upon immunization with either the Ag or the aId mAb supports that the conceptual framework proposed by Jerne finds its biologic application in the course of an immune response.  相似文献   
45.
Summary The nuclear recessive gene, chm1, of Arabidopsis thaliana is a imitator that induces a variety of plastid alterations giving rise to mixed cells and variegated leaves. The variegation is maternally transmitted but chm1 is transmitted in a Mendelian fashion (Rédei 1973; Rédei and Plurad 1973). In order to characterize the different types of plastid alterations induced by chm1, isolating homoplastidic lines, each apparently containing one type of mutant plastid in its cells, was essential since such characterization cannot be carried out on mixed cells. We have used two genetic approaches to isolate several apparently homoplastidic mutant lines by the removal of the mutator from the genetic background, and the maternal transmission of the mutant plastids. The rapidity of obtaining homoplastidic lines in the absence of chm1 indicated a non-stochastic sorting-out of plastids in mixed cells. That each of the chm1-free homoplastidic mutant lines was apparently homoplastidic for one type of mutant plastids was confirmed by electron microscopic observations. Here we report, for the first time, the production of different homoplastidic lines in the absence of the nuclear-mutator gene. Such genetically-stable homogeneous material should be a useful tool for studying the molecular mechanism(s) by which chm1 induces a variety of heritable plastid alterations.  相似文献   
46.
The interactive effects of light intensity, NaCl, nitrogen, and phosphorus on intracellular biomass content and extracellular polymeric substance production were assessed for Arthrospira sp. (Spirulina) in a two-phase culture process using principal component analysis and central composite face design. Under high light intensity (120 μmol photons m?2?s?1) and low NaCl (1 gL?1), NaNO3, and K2HPO4 (0.5 g L?1), the carbohydrate content was maximized to 26.61%. Interaction of both K2HPO4 (1.6 gL?1) and NaCl (1.19 gL?1) with low NaNO3 (0.5 gL?1) achieved the maximum content of lipids (15.62%), while high NaCl (40 gL?1), K2HPO4, and NaNO3 (4.5 gL?1) enhanced mainly total carotenoids (0.85%). Conversely, under low light intensity of 10 μmol photons m?2?s?1 combined with 11.76 gL?1 of NaCl, 0.5 gL?1 of NaNO3, and 2.68 gL?1 of K2HPO4, the phycobiliprotein content reached its highest level (16.09%). The maximum extracellular polymeric substance (EPS) production (0.902 gg?1?DW) was triggered under moderate light of 57.25 μmol photons m?2?s?1 and interaction of high NaCl (40 gL?1) and K2HPO4 (4.5 gL?1) with low NaNO3 (0.5 gL?1). The maximization ratios of intracellular biomass content in terms of carbohydrate, lipid, total carotenoid, phycobiliprotein, and EPS production were 3.55-, 1.73-, 9.55-, 2.92-, and 1.46-fold, respectively, greater than those obtained at optimal growth conditions. This study demonstrated that the multiple stress factors applied to the adopted two-phase culture process could be a promising strategy to produce biomass enriched in various high-value compound.  相似文献   
47.
In a continuing effort to discover novel TLR agonists, herein we report on the discovery and structure–activity relationship of novel tetrahydropyridopyrimidine TLR 7/8 agonists. Optimization of this series towards dual agonist activity and a high clearance profile resulted in the identification of compound 52a1. Evaluation in vivo revealed an interferon stimulated response (ISG) in mice with limited systemic exposure and demonstrated the potential in antiviral treatment or as a vaccine adjuvant.  相似文献   
48.
Bacterial superantigens, including the staphylococcal enterotoxins, are the most potent activators of T cells known and have been suggested as a causative factor in Gram-positive shock in humans. Staphylococcal enterotoxin D (SED) is dependent upon Zn2+ for high affinity interactions with MHC class II molecules and thus SED was co-crystallized with Zn2+. The crystal structure of SED has been determined in two different space groups, at 2.3 and 3.0 A resolution respectively. The three-dimensional structure of SED is similar to structures of other bacterial superantigens, although this study has revealed that SED has the unique capability of forming dimers in the presence of Zn2+. The high affinity Zn2+ site used in dimer formation is located on the surface of the beta-sheet in the C-terminal domain. Two bound metal ions are coordinated by residues from both molecules in the dimer interface and thus contribute directly to formation of the dimer. A second Zn2+ site is located on the surface close to the domain interface of the molecule. The unique feature of SED in forming a Zn2+-dependent homodimer seems to facilitate novel and biologically relevant multimeric interactions with MHC class II molecules, as shown by the induction of cytokine mRNA in human monocytes when exposed to SED and SED mutants.  相似文献   
49.
Effects of Irradiation in Genetically Coadapted Systems   总被引:5,自引:3,他引:2       下载免费PDF全文
  相似文献   
50.

Maximizing the number of offspring born per female is a key functionality trait in commercial- and/or subsistence-oriented livestock enterprises. Although the number of offspring born is closely associated with female fertility and reproductive success, the genetic control of these traits remains poorly understood in sub-Saharan Africa livestock. Using selection signature analysis performed on Ovine HD BeadChip data from the prolific Bonga sheep in Ethiopia, 41 candidate regions under selection were identified. The analysis revealed one strong selection signature on a candidate region on chromosome X spanning BMP15, suggesting this to be the primary candidate prolificacy gene in the breed. The analysis also identified several candidate regions spanning genes not reported before in prolific sheep but underlying fertility and reproduction in other species. The genes associated with female reproduction traits included SPOCK1 (age at first oestrus), GPR173 (mediator of ovarian cyclicity), HB-EGF (signalling early pregnancy success) and SMARCAL1 and HMGN3a (regulate gene expression during embryogenesis). The genes involved in male reproduction were FOXJ1 (sperm function and successful fertilization) and NME5 (spermatogenesis). We also observed genes such as PKD2L2, MAGED1 and KDM3B, which have been associated with diverse fertility traits in both sexes of other species. The results confirm the complexity of the genetic mechanisms underlying reproduction while suggesting that prolificacy in the Bonga sheep, and possibly African indigenous sheep is partly under the control of BMP15 while other genes that enhance male and female fertility are essential for reproductive fitness.

  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号